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 $57.58   6.342%   $61.2317   $61.23   $61.25   $61.20  
  Purchase #2 $111.54   12.251%   $125.2048   $125.20   $125.20   $125.20  
  Purchase #3 $149.63   11.728%   $167.1786   $167.18   $167.20   $167.20  
  Purchase #4 $132.96   11.620%   $148.41   $148.41   $148.40   $148.40  
  Purchase #5 $161.29   7.313%   $173.0851   $173.09   $173.10   $173.10  
  Purchase #6 $25.95   3.694%   $26.9086   $26.91   $26.90   $26.90  
  Purchase #7 $134.79   4.304%   $140.5914   $140.59   $140.60   $140.60  
  7 purchase totals = $773.74       $842.6102   $842.61   $842.65   $842.60