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 $102.94   8.293%   $111.4768   $111.48   $111.50   $111.50  
  Purchase #2 $204.34   5.867%   $216.3286   $216.33   $216.35   $216.30  
  Purchase #3 $89.77   6.788%   $95.8636   $95.86   $95.85   $95.90  
  Purchase #4 $141.44   4.307%   $147.5318   $147.53   $147.55   $147.50  
  Purchase #5 $106.92   7.286%   $114.7102   $114.71   $114.70   $114.70  
  Purchase #6 $211.29   8.854%   $229.9976   $230.00   $230.00   $230.00  
  Purchase #7 $99.38   7.182%   $106.5175   $106.52   $106.50   $106.50  
  7 purchase totals = $956.08       $1,022.4261   $1,022.43   $1,022.45   $1,022.40