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 $43.68   5.524%   $46.0929   $46.09   $46.10   $46.10  
  Purchase #2 $28.65   12.861%   $32.3347   $32.33   $32.35   $32.30  
  Purchase #3 $91.43   11.248%   $101.714   $101.71   $101.70   $101.70  
  Purchase #4 $41.82   12.544%   $47.0659   $47.07   $47.05   $47.10  
  Purchase #5 $115.97   5.210%   $122.012   $122.01   $122.00   $122.00  
  Purchase #6 $109.53   3.646%   $113.5235   $113.52   $113.50   $113.50  
  Purchase #7 $64.69   12.165%   $72.5595   $72.56   $72.55   $72.60  
  7 purchase totals = $495.77       $535.3025   $535.29   $535.25   $535.30