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 $228.81   8.610%   $248.5105   $248.51   $248.50   $248.50  
  Purchase #2 $151.62   6.468%   $161.4268   $161.43   $161.45   $161.40  
  Purchase #3 $106.78   12.286%   $119.899   $119.90   $119.90   $119.90  
  Purchase #4 $226.26   3.417%   $233.9913   $233.99   $234.00   $234.00  
  Purchase #5 $76.29   6.124%   $80.962   $80.96   $80.95   $81.00  
  Purchase #6 $188.90   5.810%   $199.8751   $199.88   $199.90   $199.90  
  Purchase #7 $162.29   4.374%   $169.3886   $169.39   $169.40   $169.40  
  7 purchase totals = $1,140.95       $1,214.0533   $1,214.06   $1,214.10   $1,214.10