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 $226.63   12.496%   $254.9497   $254.95   $254.95   $254.90  
  Purchase #2 $203.93   6.460%   $217.1039   $217.10   $217.10   $217.10  
  Purchase #3 $27.69   8.865%   $30.1447   $30.14   $30.15   $30.10  
  Purchase #4 $152.91   5.441%   $161.2298   $161.23   $161.25   $161.20  
  Purchase #5 $110.59   9.759%   $121.3825   $121.38   $121.40   $121.40  
  Purchase #6 $80.88   13.718%   $91.9751   $91.98   $92.00   $92.00  
  Purchase #7 $118.32   7.116%   $126.7397   $126.74   $126.75   $126.70  
  7 purchase totals = $920.95       $1,003.5254   $1,003.52   $1,003.60   $1,003.40