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 $56.95   6.728%   $60.7816   $60.78   $60.80   $60.80  
  Purchase #2 $232.66   13.704%   $264.5437   $264.54   $264.55   $264.50  
  Purchase #3 $204.54   10.507%   $226.031   $226.03   $226.05   $226.00  
  Purchase #4 $168.88   12.843%   $190.5693   $190.57   $190.55   $190.60  
  Purchase #5 $14.83   11.382%   $16.518   $16.52   $16.50   $16.50  
  Purchase #6 $116.84   11.437%   $130.203   $130.20   $130.20   $130.20  
  Purchase #7 $207.27   8.172%   $224.2081   $224.21   $224.20   $224.20  
  7 purchase totals = $1,001.97       $1,112.8547   $1,112.85   $1,112.85   $1,112.80