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 $49.27   13.487%   $55.915   $55.92   $55.90   $55.90  
  Purchase #2 $244.59   5.117%   $257.1057   $257.11   $257.10   $257.10  
  Purchase #3 $40.72   5.657%   $43.0235   $43.02   $43.00   $43.00  
  Purchase #4 $168.92   8.114%   $182.6262   $182.63   $182.65   $182.60  
  Purchase #5 $187.30   3.627%   $194.0934   $194.09   $194.10   $194.10  
  Purchase #6 $127.81   11.452%   $142.4468   $142.45   $142.45   $142.40  
  Purchase #7 $142.64   4.666%   $149.2956   $149.30   $149.30   $149.30  
  7 purchase totals = $961.25       $1,024.5062   $1,024.52   $1,024.50   $1,024.40