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 $107.71   11.167%   $119.738   $119.74   $119.75   $119.70  
  Purchase #2 $29.87   12.145%   $33.4977   $33.50   $33.50   $33.50  
  Purchase #3 $128.78   10.698%   $142.5569   $142.56   $142.55   $142.60  
  Purchase #4 $97.57   13.702%   $110.939   $110.94   $110.95   $110.90  
  Purchase #5 $62.68   5.604%   $66.1926   $66.19   $66.20   $66.20  
  Purchase #6 $210.93   8.611%   $229.0932   $229.09   $229.10   $229.10  
  Purchase #7 $132.73   8.281%   $143.7214   $143.72   $143.70   $143.70  
  7 purchase totals = $770.27       $845.7388   $845.74   $845.75   $845.70