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 $84.73   11.235%   $94.2494   $94.25   $94.25   $94.20  
  Purchase #2 $201.36   7.847%   $217.1607   $217.16   $217.15   $217.20  
  Purchase #3 $100.66   3.320%   $104.0019   $104.00   $104.00   $104.00  
  Purchase #4 $248.43   4.725%   $260.1683   $260.17   $260.15   $260.20  
  Purchase #5 $246.48   12.717%   $277.8249   $277.82   $277.80   $277.80  
  Purchase #6 $175.64   11.176%   $195.2695   $195.27   $195.25   $195.30  
  Purchase #7 $112.56   10.156%   $123.9916   $123.99   $124.00   $124.00  
  7 purchase totals = $1,169.86       $1,272.6663   $1,272.66   $1,272.60   $1,272.70