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 $54.95   8.709%   $59.7356   $59.74   $59.75   $59.70  
  Purchase #2 $235.26   6.198%   $249.8414   $249.84   $249.85   $249.80  
  Purchase #3 $32.59   3.698%   $33.7952   $33.80   $33.80   $33.80  
  Purchase #4 $159.62   8.379%   $172.9946   $172.99   $173.00   $173.00  
  Purchase #5 $162.33   10.799%   $179.86   $179.86   $179.85   $179.90  
  Purchase #6 $25.75   9.817%   $28.2779   $28.28   $28.30   $28.30  
  Purchase #7 $194.78   5.659%   $205.8026   $205.80   $205.80   $205.80  
  7 purchase totals = $865.28       $930.3073   $930.31   $930.35   $930.30