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 $64.51   4.707%   $67.5465   $67.55   $67.55   $67.50  
  Purchase #2 $125.96   10.553%   $139.2526   $139.25   $139.25   $139.30  
  Purchase #3 $199.93   5.438%   $210.8022   $210.80   $210.80   $210.80  
  Purchase #4 $97.43   6.784%   $104.0397   $104.04   $104.05   $104.00  
  Purchase #5 $94.89   12.367%   $106.625   $106.63   $106.65   $106.60  
  Purchase #6 $119.42   7.714%   $128.6321   $128.63   $128.65   $128.60  
  Purchase #7 $228.54   5.562%   $241.2514   $241.25   $241.25   $241.30  
  7 purchase totals = $930.68       $998.1495   $998.15   $998.20   $998.10