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 $152.91   6.583%   $162.9761   $162.98   $163.00   $163.00  
  Purchase #2 $86.42   7.860%   $93.2126   $93.21   $93.20   $93.20  
  Purchase #3 $225.62   8.220%   $244.166   $244.17   $244.15   $244.20  
  Purchase #4 $219.41   6.804%   $234.3387   $234.34   $234.35   $234.30  
  Purchase #5 $87.37   5.535%   $92.2059   $92.21   $92.20   $92.20  
  Purchase #6 $97.62   6.303%   $103.773   $103.77   $103.75   $103.80  
  Purchase #7 $11.64   8.782%   $12.6622   $12.66   $12.65   $12.70  
  7 purchase totals = $880.99       $943.3345   $943.34   $943.30   $943.40