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 $154.67   5.360%   $162.9603   $162.96   $162.95   $163.00  
  Purchase #2 $153.79   13.716%   $174.8838   $174.88   $174.90   $174.90  
  Purchase #3 $225.46   4.198%   $234.9248   $234.92   $234.90   $234.90  
  Purchase #4 $93.62   11.306%   $104.2047   $104.20   $104.20   $104.20  
  Purchase #5 $249.99   8.412%   $271.0192   $271.02   $271.00   $271.00  
  Purchase #6 $232.65   8.116%   $251.5319   $251.53   $251.55   $251.50  
  Purchase #7 $244.92   3.546%   $253.6049   $253.60   $253.60   $253.60  
  7 purchase totals = $1,355.10       $1,453.1296   $1,453.11   $1,453.10   $1,453.10