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 $239.37   10.223%   $263.8408   $263.84   $263.85   $263.80  
  Purchase #2 $106.83   4.581%   $111.7239   $111.72   $111.70   $111.70  
  Purchase #3 $107.73   8.527%   $116.9161   $116.92   $116.90   $116.90  
  Purchase #4 $165.69   6.596%   $176.6189   $176.62   $176.60   $176.60  
  Purchase #5 $114.67   12.462%   $128.9602   $128.96   $128.95   $129.00  
  Purchase #6 $21.26   7.402%   $22.8337   $22.83   $22.85   $22.80  
  Purchase #7 $215.42   7.345%   $231.2426   $231.24   $231.25   $231.20  
  7 purchase totals = $970.97       $1,052.1362   $1,052.13   $1,052.10   $1,052.00