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 $119.52   11.211%   $132.9194   $132.92   $132.90   $132.90  
  Purchase #2 $57.49   7.532%   $61.8201   $61.82   $61.80   $61.80  
  Purchase #3 $83.42   13.743%   $94.8844   $94.88   $94.90   $94.90  
  Purchase #4 $96.66   5.628%   $102.1   $102.10   $102.10   $102.10  
  Purchase #5 $213.47   12.503%   $240.1602   $240.16   $240.15   $240.20  
  Purchase #6 $94.98   3.131%   $97.9538   $97.95   $97.95   $98.00  
  Purchase #7 $122.94   9.199%   $134.2493   $134.25   $134.25   $134.20  
  7 purchase totals = $788.48       $864.0872   $864.08   $864.05   $864.10