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 $197.81   13.171%   $223.8636   $223.86   $223.85   $223.90  
  Purchase #2 $70.93   8.502%   $76.9605   $76.96   $76.95   $77.00  
  Purchase #3 $28.86   10.104%   $31.776   $31.78   $31.80   $31.80  
  Purchase #4 $96.34   8.726%   $104.7466   $104.75   $104.75   $104.70  
  Purchase #5 $154.61   11.500%   $172.3902   $172.39   $172.40   $172.40  
  Purchase #6 $202.75   9.472%   $221.9545   $221.95   $221.95   $222.00  
  Purchase #7 $53.55   5.558%   $56.5263   $56.53   $56.55   $56.50  
  7 purchase totals = $804.85       $888.2177   $888.22   $888.25   $888.30