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 $224.82   7.625%   $241.9625   $241.96   $241.95   $242.00  
  Purchase #2 $48.57   7.772%   $52.3449   $52.34   $52.35   $52.30  
  Purchase #3 $146.26   3.191%   $150.9272   $150.93   $150.95   $150.90  
  Purchase #4 $50.72   13.804%   $57.7214   $57.72   $57.70   $57.70  
  Purchase #5 $177.36   10.426%   $195.8516   $195.85   $195.85   $195.90  
  Purchase #6 $247.78   8.268%   $268.2665   $268.27   $268.25   $268.30  
  Purchase #7 $53.52   5.107%   $56.2533   $56.25   $56.25   $56.30  
  7 purchase totals = $949.03       $1,023.3274   $1,023.32   $1,023.30   $1,023.40