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 $74.71   9.790%   $82.0241   $82.02   $82.00   $82.00  
  Purchase #2 $151.46   3.357%   $156.5445   $156.54   $156.55   $156.50  
  Purchase #3 $65.53   11.855%   $73.2986   $73.30   $73.30   $73.30  
  Purchase #4 $182.64   10.306%   $201.4629   $201.46   $201.45   $201.50  
  Purchase #5 $218.83   5.405%   $230.6578   $230.66   $230.65   $230.70  
  Purchase #6 $107.35   3.323%   $110.9172   $110.92   $110.90   $110.90  
  Purchase #7 $55.99   10.848%   $62.0638   $62.06   $62.05   $62.10  
  7 purchase totals = $856.51       $916.9689   $916.96   $916.90   $917.00