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 $106.80   9.184%   $116.6085   $116.61   $116.60   $116.60  
  Purchase #2 $77.97   9.479%   $85.3608   $85.36   $85.35   $85.40  
  Purchase #3 $164.57   9.806%   $180.7077   $180.71   $180.70   $180.70  
  Purchase #4 $95.59   7.262%   $102.5317   $102.53   $102.55   $102.50  
  Purchase #5 $87.92   12.820%   $99.1913   $99.19   $99.20   $99.20  
  Purchase #6 $233.92   5.195%   $246.0721   $246.07   $246.05   $246.10  
  Purchase #7 $127.65   9.294%   $139.5138   $139.51   $139.50   $139.50  
  7 purchase totals = $894.42       $969.9859   $969.98   $969.95   $970.00