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 $83.26   6.637%   $88.786   $88.79   $88.80   $88.80  
  Purchase #2 $53.49   10.461%   $59.0856   $59.09   $59.10   $59.10  
  Purchase #3 $94.39   3.802%   $97.9787   $97.98   $98.00   $98.00  
  Purchase #4 $48.35   13.807%   $55.0257   $55.03   $55.05   $55.00  
  Purchase #5 $238.68   11.279%   $265.6007   $265.60   $265.60   $265.60  
  Purchase #6 $79.54   11.669%   $88.8215   $88.82   $88.80   $88.80  
  Purchase #7 $216.35   11.708%   $241.6803   $241.68   $241.70   $241.70  
  7 purchase totals = $814.06       $896.9785   $896.99   $897.05   $897.00