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 $241.73   4.721%   $253.1421   $253.14   $253.15   $253.10  
  Purchase #2 $114.72   9.791%   $125.9522   $125.95   $125.95   $126.00  
  Purchase #3 $160.77   9.817%   $176.5528   $176.55   $176.55   $176.60  
  Purchase #4 $95.75   6.602%   $102.0714   $102.07   $102.05   $102.10  
  Purchase #5 $221.73   5.801%   $234.5926   $234.59   $234.60   $234.60  
  Purchase #6 $185.40   9.823%   $203.6118   $203.61   $203.60   $203.60  
  Purchase #7 $35.42   11.304%   $39.4239   $39.42   $39.40   $39.40  
  7 purchase totals = $1,055.52       $1,135.3468   $1,135.33   $1,135.30   $1,135.40