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 $68.75   3.698%   $71.2924   $71.29   $71.30   $71.30  
  Purchase #2 $152.34   5.228%   $160.3043   $160.30   $160.30   $160.30  
  Purchase #3 $167.45   12.514%   $188.4047   $188.40   $188.40   $188.40  
  Purchase #4 $178.66   11.866%   $199.8598   $199.86   $199.85   $199.90  
  Purchase #5 $96.65   7.275%   $103.6813   $103.68   $103.70   $103.70  
  Purchase #6 $249.27   7.519%   $268.0126   $268.01   $268.00   $268.00  
  Purchase #7 $152.91   13.277%   $173.2119   $173.21   $173.20   $173.20  
  7 purchase totals = $1,066.03       $1,164.7670   $1,164.75   $1,164.75   $1,164.80