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 $86.54   9.644%   $94.8859   $94.89   $94.90   $94.90  
  Purchase #2 $242.59   12.384%   $272.6323   $272.63   $272.65   $272.60  
  Purchase #3 $153.61   3.307%   $158.6899   $158.69   $158.70   $158.70  
  Purchase #4 $184.37   13.474%   $209.212   $209.21   $209.20   $209.20  
  Purchase #5 $235.69   13.340%   $267.131   $267.13   $267.15   $267.10  
  Purchase #6 $104.51   11.294%   $116.3134   $116.31   $116.30   $116.30  
  Purchase #7 $223.87   9.183%   $244.428   $244.43   $244.45   $244.40  
  7 purchase totals = $1,231.18       $1,363.2925   $1,363.29   $1,363.35   $1,363.20