Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $214.29   10.415%   $236.6083   $236.61   $236.60   $236.60  
  Purchase #2 $147.84   9.800%   $162.3283   $162.33   $162.35   $162.30  
  Purchase #3 $106.85   10.693%   $118.2755   $118.28   $118.30   $118.30  
  Purchase #4 $205.52   4.767%   $215.3171   $215.32   $215.30   $215.30  
  Purchase #5 $215.73   11.710%   $240.992   $240.99   $241.00   $241.00  
  Purchase #6 $197.63   13.540%   $224.3891   $224.39   $224.40   $224.40  
  Purchase #7 $198.54   12.721%   $223.7963   $223.80   $223.80   $223.80  
  7 purchase totals = $1,286.40       $1,421.7066   $1,421.72   $1,421.75   $1,421.70