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 $125.63   12.837%   $141.7571   $141.76   $141.75   $141.80  
  Purchase #2 $147.53   4.744%   $154.5288   $154.53   $154.55   $154.50  
  Purchase #3 $25.83   4.552%   $27.0058   $27.01   $27.00   $27.00  
  Purchase #4 $217.57   7.458%   $233.7964   $233.80   $233.80   $233.80  
  Purchase #5 $20.59   3.838%   $21.3802   $21.38   $21.40   $21.40  
  Purchase #6 $187.76   5.585%   $198.2464   $198.25   $198.25   $198.20  
  Purchase #7 $70.76   10.512%   $78.1983   $78.20   $78.20   $78.20  
  7 purchase totals = $795.67       $854.9130   $854.93   $854.95   $854.90