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 $88.26   6.398%   $93.9069   $93.91   $93.90   $93.90  
  Purchase #2 $224.62   8.754%   $244.2832   $244.28   $244.30   $244.30  
  Purchase #3 $59.74   13.362%   $67.7225   $67.72   $67.70   $67.70  
  Purchase #4 $166.67   7.200%   $178.6702   $178.67   $178.65   $178.70  
  Purchase #5 $226.58   5.352%   $238.7066   $238.71   $238.70   $238.70  
  Purchase #6 $42.96   7.189%   $46.0484   $46.05   $46.05   $46.00  
  Purchase #7 $173.26   8.497%   $187.9819   $187.98   $188.00   $188.00  
  7 purchase totals = $982.09       $1,057.3197   $1,057.32   $1,057.30   $1,057.30