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 $168.54   13.603%   $191.4665   $191.47   $191.45   $191.50  
  Purchase #2 $155.36   12.761%   $175.1855   $175.19   $175.20   $175.20  
  Purchase #3 $117.25   7.804%   $126.4002   $126.40   $126.40   $126.40  
  Purchase #4 $62.44   5.323%   $65.7637   $65.76   $65.75   $65.80  
  Purchase #5 $141.73   11.539%   $158.0842   $158.08   $158.10   $158.10  
  Purchase #6 $131.27   4.691%   $137.4279   $137.43   $137.45   $137.40  
  Purchase #7 $216.32   3.829%   $224.6029   $224.60   $224.60   $224.60  
  7 purchase totals = $992.91       $1,078.9309   $1,078.93   $1,078.95   $1,079.00