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 $65.89   13.836%   $75.0065   $75.01   $75.00   $75.00  
  Purchase #2 $214.89   13.234%   $243.3285   $243.33   $243.35   $243.30  
  Purchase #3 $207.44   8.291%   $224.6389   $224.64   $224.65   $224.60  
  Purchase #4 $33.27   3.136%   $34.3133   $34.31   $34.30   $34.30  
  Purchase #5 $217.38   11.116%   $241.544   $241.54   $241.55   $241.50  
  Purchase #6 $201.89   3.201%   $208.3525   $208.35   $208.35   $208.40  
  Purchase #7 $49.68   12.355%   $55.818   $55.82   $55.80   $55.80  
  7 purchase totals = $990.44       $1,083.0017   $1,083.00   $1,083.00   $1,082.90