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 $60.89   12.544%   $68.528   $68.53   $68.55   $68.50  
  Purchase #2 $173.51   4.315%   $180.997   $181.00   $181.00   $181.00  
  Purchase #3 $183.51   10.545%   $202.8611   $202.86   $202.85   $202.90  
  Purchase #4 $191.66   5.787%   $202.7514   $202.75   $202.75   $202.80  
  Purchase #5 $93.88   11.213%   $104.4068   $104.41   $104.40   $104.40  
  Purchase #6 $26.72   6.279%   $28.3977   $28.40   $28.40   $28.40  
  Purchase #7 $185.46   12.419%   $208.4923   $208.49   $208.50   $208.50  
  7 purchase totals = $915.63       $996.4343   $996.44   $996.45   $996.50