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 $194.46   8.553%   $211.0922   $211.09   $211.10   $211.10  
  Purchase #2 $41.41   5.381%   $43.6383   $43.64   $43.65   $43.60  
  Purchase #3 $48.32   11.631%   $53.9401   $53.94   $53.95   $53.90  
  Purchase #4 $223.48   5.252%   $235.2172   $235.22   $235.20   $235.20  
  Purchase #5 $108.76   10.705%   $120.4028   $120.40   $120.40   $120.40  
  Purchase #6 $68.79   10.869%   $76.2668   $76.27   $76.25   $76.30  
  Purchase #7 $209.59   6.843%   $223.9322   $223.93   $223.95   $223.90  
  7 purchase totals = $894.81       $964.4896   $964.49   $964.50   $964.40