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 $61.77   4.356%   $64.4607   $64.46   $64.45   $64.50  
  Purchase #2 $192.26   6.790%   $205.3145   $205.31   $205.30   $205.30  
  Purchase #3 $86.95   3.445%   $89.9454   $89.95   $89.95   $89.90  
  Purchase #4 $215.78   11.842%   $241.3327   $241.33   $241.35   $241.30  
  Purchase #5 $198.75   4.406%   $207.5069   $207.51   $207.50   $207.50  
  Purchase #6 $192.49   6.472%   $204.948   $204.95   $204.95   $204.90  
  Purchase #7 $203.42   6.715%   $217.0797   $217.08   $217.10   $217.10  
  7 purchase totals = $1,151.42       $1,230.5879   $1,230.59   $1,230.60   $1,230.50