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 $68.59   13.197%   $77.6418   $77.64   $77.65   $77.60  
  Purchase #2 $122.39   6.569%   $130.4298   $130.43   $130.45   $130.40  
  Purchase #3 $167.29   3.598%   $173.3091   $173.31   $173.30   $173.30  
  Purchase #4 $26.32   8.413%   $28.5343   $28.53   $28.55   $28.50  
  Purchase #5 $148.92   8.786%   $162.0041   $162.00   $162.00   $162.00  
  Purchase #6 $125.62   12.573%   $141.4142   $141.41   $141.40   $141.40  
  Purchase #7 $91.76   3.584%   $95.0487   $95.05   $95.05   $95.00  
  7 purchase totals = $750.89       $808.3820   $808.37   $808.40   $808.20