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 $136.68   13.529%   $155.1714   $155.17   $155.15   $155.20  
  Purchase #2 $79.84   7.726%   $86.0084   $86.01   $86.00   $86.00  
  Purchase #3 $248.85   4.844%   $260.9043   $260.90   $260.90   $260.90  
  Purchase #4 $32.93   10.116%   $36.2612   $36.26   $36.25   $36.30  
  Purchase #5 $95.52   9.199%   $104.3069   $104.31   $104.30   $104.30  
  Purchase #6 $232.69   3.642%   $241.1646   $241.16   $241.15   $241.20  
  Purchase #7 $62.78   6.453%   $66.8312   $66.83   $66.85   $66.80  
  7 purchase totals = $889.29       $950.6480   $950.64   $950.60   $950.70