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 $169.62   12.681%   $191.1295   $191.13   $191.15   $191.10  
  Purchase #2 $248.41   7.415%   $266.8296   $266.83   $266.85   $266.80  
  Purchase #3 $150.67   9.556%   $165.068   $165.07   $165.05   $165.10  
  Purchase #4 $198.58   9.276%   $217.0003   $217.00   $217.00   $217.00  
  Purchase #5 $215.39   8.851%   $234.4542   $234.45   $234.45   $234.50  
  Purchase #6 $95.82   10.774%   $106.1436   $106.14   $106.15   $106.10  
  Purchase #7 $143.33   10.694%   $158.6577   $158.66   $158.65   $158.70  
  7 purchase totals = $1,221.82       $1,339.2829   $1,339.28   $1,339.30   $1,339.30