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 $161.68   13.530%   $183.5553   $183.56   $183.55   $183.60  
  Purchase #2 $57.33   11.660%   $64.0147   $64.01   $64.00   $64.00  
  Purchase #3 $38.52   6.548%   $41.0423   $41.04   $41.05   $41.00  
  Purchase #4 $87.26   11.456%   $97.2565   $97.26   $97.25   $97.30  
  Purchase #5 $122.72   9.427%   $134.2888   $134.29   $134.30   $134.30  
  Purchase #6 $204.86   11.293%   $227.9948   $227.99   $228.00   $228.00  
  Purchase #7 $125.83   8.259%   $136.2223   $136.22   $136.20   $136.20  
  7 purchase totals = $798.20       $884.3747   $884.37   $884.35   $884.40