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 $212.73   13.506%   $241.4613   $241.46   $241.45   $241.50  
  Purchase #2 $114.99   4.582%   $120.2588   $120.26   $120.25   $120.30  
  Purchase #3 $23.39   10.836%   $25.9245   $25.92   $25.90   $25.90  
  Purchase #4 $18.72   3.134%   $19.3067   $19.31   $19.30   $19.30  
  Purchase #5 $190.48   10.107%   $209.7318   $209.73   $209.75   $209.70  
  Purchase #6 $172.47   7.680%   $185.7157   $185.72   $185.70   $185.70  
  Purchase #7 $217.84   6.398%   $231.7774   $231.78   $231.80   $231.80  
  7 purchase totals = $950.62       $1,034.1762   $1,034.18   $1,034.15   $1,034.20