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 $228.95   11.470%   $255.2106   $255.21   $255.20   $255.20  
  Purchase #2 $59.71   12.133%   $66.9546   $66.95   $66.95   $67.00  
  Purchase #3 $49.60   3.807%   $51.4883   $51.49   $51.50   $51.50  
  Purchase #4 $199.79   6.257%   $212.2909   $212.29   $212.30   $212.30  
  Purchase #5 $182.25   5.348%   $191.9967   $192.00   $192.00   $192.00  
  Purchase #6 $173.78   7.764%   $187.2723   $187.27   $187.25   $187.30  
  Purchase #7 $58.74   11.371%   $65.4193   $65.42   $65.40   $65.40  
  7 purchase totals = $952.82       $1,030.6327   $1,030.63   $1,030.60   $1,030.70