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 $28.77   13.821%   $32.7463   $32.75   $32.75   $32.70  
  Purchase #2 $198.75   4.574%   $207.8408   $207.84   $207.85   $207.80  
  Purchase #3 $228.73   11.223%   $254.4004   $254.40   $254.40   $254.40  
  Purchase #4 $88.82   9.490%   $97.249   $97.25   $97.25   $97.20  
  Purchase #5 $195.33   8.825%   $212.5679   $212.57   $212.55   $212.60  
  Purchase #6 $154.37   11.607%   $172.2877   $172.29   $172.30   $172.30  
  Purchase #7 $227.77   5.569%   $240.4545   $240.45   $240.45   $240.50  
  7 purchase totals = $1,122.54       $1,217.5466   $1,217.55   $1,217.55   $1,217.50