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 $186.72   6.581%   $199.008   $199.01   $199.00   $199.00  
  Purchase #2 $64.50   7.139%   $69.1047   $69.10   $69.10   $69.10  
  Purchase #3 $81.55   4.724%   $85.4024   $85.40   $85.40   $85.40  
  Purchase #4 $61.62   5.707%   $65.1367   $65.14   $65.15   $65.10  
  Purchase #5 $100.91   4.212%   $105.1603   $105.16   $105.15   $105.20  
  Purchase #6 $92.29   10.133%   $101.6417   $101.64   $101.65   $101.60  
  Purchase #7 $164.70   9.473%   $180.302   $180.30   $180.30   $180.30  
  7 purchase totals = $752.29       $805.7558   $805.75   $805.75   $805.70