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 $156.28   4.784%   $163.7564   $163.76   $163.75   $163.80  
  Purchase #2 $224.55   8.471%   $243.5716   $243.57   $243.55   $243.60  
  Purchase #3 $65.83   5.474%   $69.4335   $69.43   $69.45   $69.40  
  Purchase #4 $228.66   11.828%   $255.7059   $255.71   $255.70   $255.70  
  Purchase #5 $178.98   11.583%   $199.7113   $199.71   $199.70   $199.70  
  Purchase #6 $60.99   6.432%   $64.9129   $64.91   $64.90   $64.90  
  Purchase #7 $223.72   11.540%   $249.5373   $249.54   $249.55   $249.50  
  7 purchase totals = $1,139.01       $1,246.6289   $1,246.63   $1,246.60   $1,246.60