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 $40.89   12.528%   $46.0127   $46.01   $46.00   $46.00  
  Purchase #2 $159.67   6.257%   $169.6606   $169.66   $169.65   $169.70  
  Purchase #3 $212.71   5.394%   $224.1836   $224.18   $224.20   $224.20  
  Purchase #4 $242.94   10.278%   $267.9094   $267.91   $267.90   $267.90  
  Purchase #5 $68.34   9.534%   $74.8555   $74.86   $74.85   $74.90  
  Purchase #6 $54.56   4.591%   $57.0648   $57.06   $57.05   $57.10  
  Purchase #7 $169.45   9.204%   $185.0462   $185.05   $185.05   $185.00  
  7 purchase totals = $948.56       $1,024.7328   $1,024.73   $1,024.70   $1,024.80