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 $67.62   8.400%   $73.3001   $73.30   $73.30   $73.30  
  Purchase #2 $53.44   12.751%   $60.2541   $60.25   $60.25   $60.30  
  Purchase #3 $116.46   13.679%   $132.3906   $132.39   $132.40   $132.40  
  Purchase #4 $124.97   6.625%   $133.2493   $133.25   $133.25   $133.20  
  Purchase #5 $151.86   9.782%   $166.7149   $166.71   $166.70   $166.70  
  Purchase #6 $33.60   13.401%   $38.1027   $38.10   $38.10   $38.10  
  Purchase #7 $125.90   7.197%   $134.961   $134.96   $134.95   $135.00  
  7 purchase totals = $673.85       $738.9727   $738.96   $738.95   $739.00