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 $216.57   11.421%   $241.3045   $241.30   $241.30   $241.30  
  Purchase #2 $83.66   6.158%   $88.8118   $88.81   $88.80   $88.80  
  Purchase #3 $123.92   11.600%   $138.2947   $138.29   $138.30   $138.30  
  Purchase #4 $200.46   8.274%   $217.0461   $217.05   $217.05   $217.00  
  Purchase #5 $43.37   6.386%   $46.1396   $46.14   $46.15   $46.10  
  Purchase #6 $193.84   3.751%   $201.1109   $201.11   $201.10   $201.10  
  Purchase #7 $59.52   3.102%   $61.3663   $61.37   $61.35   $61.40  
  7 purchase totals = $921.34       $994.0739   $994.07   $994.05   $994.00