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 $59.57   4.162%   $62.0493   $62.05   $62.05   $62.00  
  Purchase #2 $207.97   10.576%   $229.9649   $229.96   $229.95   $230.00  
  Purchase #3 $159.41   12.375%   $179.137   $179.14   $179.15   $179.10  
  Purchase #4 $71.32   8.424%   $77.328   $77.33   $77.35   $77.30  
  Purchase #5 $18.68   4.107%   $19.4472   $19.45   $19.45   $19.40  
  Purchase #6 $146.70   10.862%   $162.6346   $162.63   $162.65   $162.60  
  Purchase #7 $237.40   11.496%   $264.6915   $264.69   $264.70   $264.70  
  7 purchase totals = $901.05       $995.2525   $995.25   $995.30   $995.10