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 $211.34   11.107%   $234.8135   $234.81   $234.80   $234.80  
  Purchase #2 $98.50   8.298%   $106.6735   $106.67   $106.65   $106.70  
  Purchase #3 $73.57   6.193%   $78.1262   $78.13   $78.15   $78.10  
  Purchase #4 $69.46   13.526%   $78.8552   $78.86   $78.85   $78.90  
  Purchase #5 $99.86   7.838%   $107.687   $107.69   $107.70   $107.70  
  Purchase #6 $183.39   6.493%   $195.2975   $195.30   $195.30   $195.30  
  Purchase #7 $220.29   5.275%   $231.9103   $231.91   $231.90   $231.90  
  7 purchase totals = $956.41       $1,033.3632   $1,033.37   $1,033.35   $1,033.40