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 $28.46   13.635%   $32.3405   $32.34   $32.35   $32.30  
  Purchase #2 $234.61   6.382%   $249.5828   $249.58   $249.60   $249.60  
  Purchase #3 $122.97   7.356%   $132.0157   $132.02   $132.00   $132.00  
  Purchase #4 $72.70   9.844%   $79.8566   $79.86   $79.85   $79.90  
  Purchase #5 $64.29   11.375%   $71.603   $71.60   $71.60   $71.60  
  Purchase #6 $126.87   6.485%   $135.0975   $135.10   $135.10   $135.10  
  Purchase #7 $249.99   4.130%   $260.3146   $260.31   $260.30   $260.30  
  7 purchase totals = $899.89       $960.8107   $960.81   $960.80   $960.80