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 $206.46   3.147%   $212.9573   $212.96   $212.95   $213.00  
  Purchase #2 $120.40   3.619%   $124.7573   $124.76   $124.75   $124.80  
  Purchase #3 $125.28   12.553%   $141.0064   $141.01   $141.00   $141.00  
  Purchase #4 $45.96   4.814%   $48.1725   $48.17   $48.15   $48.20  
  Purchase #5 $105.71   5.750%   $111.7883   $111.79   $111.80   $111.80  
  Purchase #6 $244.92   8.381%   $265.4467   $265.45   $265.45   $265.40  
  Purchase #7 $177.39   9.682%   $194.5649   $194.56   $194.55   $194.60  
  7 purchase totals = $1,026.12       $1,098.6934   $1,098.70   $1,098.65   $1,098.80