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 $42.26   10.226%   $46.5815   $46.58   $46.60   $46.60  
  Purchase #2 $182.67   4.703%   $191.261   $191.26   $191.25   $191.30  
  Purchase #3 $52.64   6.150%   $55.8774   $55.88   $55.90   $55.90  
  Purchase #4 $125.45   6.684%   $133.8351   $133.84   $133.85   $133.80  
  Purchase #5 $209.90   11.774%   $234.6136   $234.61   $234.60   $234.60  
  Purchase #6 $23.44   8.801%   $25.503   $25.50   $25.50   $25.50  
  Purchase #7 $107.61   5.491%   $113.5189   $113.52   $113.50   $113.50  
  7 purchase totals = $743.97       $801.1905   $801.19   $801.20   $801.20