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 $207.56   6.715%   $221.4977   $221.50   $221.50   $221.50  
  Purchase #2 $227.39   4.155%   $236.8381   $236.84   $236.85   $236.80  
  Purchase #3 $48.42   11.480%   $53.9786   $53.98   $54.00   $54.00  
  Purchase #4 $45.31   8.307%   $49.0739   $49.07   $49.05   $49.10  
  Purchase #5 $60.40   6.820%   $64.5193   $64.52   $64.50   $64.50  
  Purchase #6 $103.35   9.579%   $113.2499   $113.25   $113.25   $113.20  
  Purchase #7 $223.98   4.541%   $234.1509   $234.15   $234.15   $234.20  
  7 purchase totals = $916.41       $973.3084   $973.31   $973.30   $973.30