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 $38.56   11.560%   $43.0175   $43.02   $43.00   $43.00  
  Purchase #2 $64.86   12.519%   $72.9798   $72.98   $73.00   $73.00  
  Purchase #3 $236.71   5.610%   $249.9894   $249.99   $250.00   $250.00  
  Purchase #4 $134.52   5.135%   $141.4276   $141.43   $141.45   $141.40  
  Purchase #5 $73.49   3.804%   $76.2856   $76.29   $76.30   $76.30  
  Purchase #6 $174.45   12.356%   $196.005   $196.01   $196.00   $196.00  
  Purchase #7 $158.77   5.824%   $168.0168   $168.02   $168.00   $168.00  
  7 purchase totals = $881.36       $947.7217   $947.74   $947.75   $947.70