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 $224.80   10.303%   $247.9611   $247.96   $247.95   $248.00  
  Purchase #2 $93.93   10.532%   $103.8227   $103.82   $103.80   $103.80  
  Purchase #3 $96.40   3.457%   $99.7325   $99.73   $99.75   $99.70  
  Purchase #4 $92.81   3.808%   $96.3442   $96.34   $96.35   $96.30  
  Purchase #5 $224.51   10.382%   $247.8186   $247.82   $247.80   $247.80  
  Purchase #6 $222.30   6.147%   $235.9648   $235.96   $235.95   $236.00  
  Purchase #7 $22.27   10.461%   $24.5997   $24.60   $24.60   $24.60  
  7 purchase totals = $977.02       $1,056.2436   $1,056.23   $1,056.20   $1,056.20