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 $31.98   11.853%   $35.7706   $35.77   $35.75   $35.80  
  Purchase #2 $232.76   10.277%   $256.6807   $256.68   $256.70   $256.70  
  Purchase #3 $154.55   13.424%   $175.2968   $175.30   $175.30   $175.30  
  Purchase #4 $173.85   9.232%   $189.8998   $189.90   $189.90   $189.90  
  Purchase #5 $163.99   8.183%   $177.4093   $177.41   $177.40   $177.40  
  Purchase #6 $111.96   11.399%   $124.7223   $124.72   $124.70   $124.70  
  Purchase #7 $217.57   11.548%   $242.695   $242.70   $242.70   $242.70  
  7 purchase totals = $1,086.66       $1,202.4745   $1,202.48   $1,202.45   $1,202.50