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 $87.91   8.454%   $95.3419   $95.34   $95.35   $95.30  
  Purchase #2 $138.37   10.325%   $152.6567   $152.66   $152.65   $152.70  
  Purchase #3 $191.27   13.856%   $217.7724   $217.77   $217.75   $217.80  
  Purchase #4 $189.53   12.188%   $212.6299   $212.63   $212.65   $212.60  
  Purchase #5 $148.35   11.549%   $165.4829   $165.48   $165.50   $165.50  
  Purchase #6 $101.83   10.761%   $112.7879   $112.79   $112.80   $112.80  
  Purchase #7 $238.76   5.220%   $251.2233   $251.22   $251.20   $251.20  
  7 purchase totals = $1,096.02       $1,207.8950   $1,207.89   $1,207.90   $1,207.90