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 $61.41   6.646%   $65.4913   $65.49   $65.50   $65.50  
  Purchase #2 $149.87   11.503%   $167.1095   $167.11   $167.10   $167.10  
  Purchase #3 $89.84   4.169%   $93.5854   $93.59   $93.60   $93.60  
  Purchase #4 $175.70   11.184%   $195.3503   $195.35   $195.35   $195.40  
  Purchase #5 $244.60   4.302%   $255.1227   $255.12   $255.10   $255.10  
  Purchase #6 $118.97   3.171%   $122.7425   $122.74   $122.75   $122.70  
  Purchase #7 $221.30   5.803%   $234.142   $234.14   $234.15   $234.10  
  7 purchase totals = $1,061.69       $1,133.5437   $1,133.54   $1,133.55   $1,133.50