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 $173.77   10.655%   $192.2852   $192.29   $192.30   $192.30  
  Purchase #2 $219.58   11.103%   $243.96   $243.96   $243.95   $244.00  
  Purchase #3 $70.66   4.601%   $73.9111   $73.91   $73.90   $73.90  
  Purchase #4 $172.76   12.391%   $194.1667   $194.17   $194.15   $194.20  
  Purchase #5 $139.60   8.614%   $151.6251   $151.63   $151.65   $151.60  
  Purchase #6 $6.57   4.546%   $6.8687   $6.87   $6.85   $6.90  
  Purchase #7 $106.48   11.796%   $119.0404   $119.04   $119.05   $119.00  
  7 purchase totals = $889.42       $981.8572   $981.87   $981.85   $981.90