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 $224.86   8.172%   $243.2356   $243.24   $243.25   $243.20  
  Purchase #2 $77.83   6.617%   $82.98   $82.98   $83.00   $83.00  
  Purchase #3 $57.91   13.852%   $65.9317   $65.93   $65.95   $65.90  
  Purchase #4 $187.30   3.809%   $194.4343   $194.43   $194.45   $194.40  
  Purchase #5 $127.90   6.215%   $135.849   $135.85   $135.85   $135.80  
  Purchase #6 $140.53   9.824%   $154.3357   $154.34   $154.35   $154.30  
  Purchase #7 $7.39   5.232%   $7.7766   $7.78   $7.80   $7.80  
  7 purchase totals = $823.72       $884.5429   $884.55   $884.65   $884.40