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 $234.81   13.823%   $267.2678   $267.27   $267.25   $267.30  
  Purchase #2 $110.92   5.257%   $116.7511   $116.75   $116.75   $116.80  
  Purchase #3 $234.65   10.739%   $259.8491   $259.85   $259.85   $259.80  
  Purchase #4 $80.42   9.797%   $88.2987   $88.30   $88.30   $88.30  
  Purchase #5 $139.50   3.734%   $144.7089   $144.71   $144.70   $144.70  
  Purchase #6 $173.89   3.265%   $179.5675   $179.57   $179.55   $179.60  
  Purchase #7 $110.82   7.768%   $119.4285   $119.43   $119.45   $119.40  
  7 purchase totals = $1,085.01       $1,175.8716   $1,175.88   $1,175.85   $1,175.90