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 $199.42   12.465%   $224.2777   $224.28   $224.30   $224.30  
  Purchase #2 $212.41   12.312%   $238.5619   $238.56   $238.55   $238.60  
  Purchase #3 $159.83   11.793%   $178.6788   $178.68   $178.70   $178.70  
  Purchase #4 $95.84   6.155%   $101.739   $101.74   $101.75   $101.70  
  Purchase #5 $181.41   10.201%   $199.9156   $199.92   $199.90   $199.90  
  Purchase #6 $68.55   11.630%   $76.5224   $76.52   $76.50   $76.50  
  Purchase #7 $80.39   6.428%   $85.5575   $85.56   $85.55   $85.60  
  7 purchase totals = $997.85       $1,105.2529   $1,105.26   $1,105.25   $1,105.30