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 $23.47   10.338%   $25.8963   $25.90   $25.90   $25.90  
  Purchase #2 $157.40   13.130%   $178.0666   $178.07   $178.05   $178.10  
  Purchase #3 $204.92   4.248%   $213.625   $213.63   $213.65   $213.60  
  Purchase #4 $181.85   11.205%   $202.2263   $202.23   $202.25   $202.20  
  Purchase #5 $65.66   11.590%   $73.27   $73.27   $73.25   $73.30  
  Purchase #6 $102.31   6.607%   $109.0696   $109.07   $109.05   $109.10  
  Purchase #7 $32.48   4.667%   $33.9958   $34.00   $34.00   $34.00  
  7 purchase totals = $768.09       $836.1496   $836.17   $836.15   $836.20