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 $35.59   13.310%   $40.327   $40.33   $40.35   $40.30  
  Purchase #2 $165.26   6.491%   $175.987   $175.99   $176.00   $176.00  
  Purchase #3 $30.67   5.687%   $32.4142   $32.41   $32.40   $32.40  
  Purchase #4 $160.32   12.585%   $180.4963   $180.50   $180.50   $180.50  
  Purchase #5 $78.68   6.107%   $83.485   $83.49   $83.50   $83.50  
  Purchase #6 $32.33   13.215%   $36.6024   $36.60   $36.60   $36.60  
  Purchase #7 $241.73   6.720%   $257.9743   $257.97   $257.95   $258.00  
  7 purchase totals = $744.58       $807.2862   $807.29   $807.30   $807.30