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 $154.63   7.412%   $166.0912   $166.09   $166.10   $166.10  
  Purchase #2 $64.45   12.338%   $72.4018   $72.40   $72.40   $72.40  
  Purchase #3 $134.73   13.589%   $153.0385   $153.04   $153.05   $153.00  
  Purchase #4 $108.56   8.586%   $117.881   $117.88   $117.90   $117.90  
  Purchase #5 $240.59   8.461%   $260.9463   $260.95   $260.95   $260.90  
  Purchase #6 $248.26   7.798%   $267.6193   $267.62   $267.60   $267.60  
  Purchase #7 $9.96   10.420%   $10.9978   $11.00   $11.00   $11.00  
  7 purchase totals = $961.18       $1,048.9759   $1,048.98   $1,049.00   $1,048.90