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 $249.25   10.624%   $275.7303   $275.73   $275.75   $275.70  
  Purchase #2 $73.59   4.788%   $77.1135   $77.11   $77.10   $77.10  
  Purchase #3 $86.32   8.753%   $93.8756   $93.88   $93.90   $93.90  
  Purchase #4 $106.58   11.494%   $118.8303   $118.83   $118.85   $118.80  
  Purchase #5 $144.84   8.827%   $157.625   $157.63   $157.65   $157.60  
  Purchase #6 $115.63   4.513%   $120.8484   $120.85   $120.85   $120.80  
  Purchase #7 $157.32   9.579%   $172.3897   $172.39   $172.40   $172.40  
  7 purchase totals = $933.53       $1,016.4128   $1,016.42   $1,016.50   $1,016.30