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 $64.34   11.341%   $71.6368   $71.64   $71.65   $71.60  
  Purchase #2 $208.47   12.179%   $233.8596   $233.86   $233.85   $233.90  
  Purchase #3 $133.95   13.167%   $151.5872   $151.59   $151.60   $151.60  
  Purchase #4 $166.92   5.386%   $175.9103   $175.91   $175.90   $175.90  
  Purchase #5 $229.26   12.565%   $258.0665   $258.07   $258.05   $258.10  
  Purchase #6 $141.84   6.489%   $151.044   $151.04   $151.05   $151.00  
  Purchase #7 $195.87   11.489%   $218.3735   $218.37   $218.35   $218.40  
  7 purchase totals = $1,140.65       $1,260.4779   $1,260.48   $1,260.45   $1,260.50