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 $239.69   12.620%   $269.9389   $269.94   $269.95   $269.90  
  Purchase #2 $225.85   11.676%   $252.2202   $252.22   $252.20   $252.20  
  Purchase #3 $218.40   4.337%   $227.872   $227.87   $227.85   $227.90  
  Purchase #4 $101.96   9.123%   $111.2618   $111.26   $111.25   $111.30  
  Purchase #5 $59.34   12.397%   $66.6964   $66.70   $66.70   $66.70  
  Purchase #6 $93.25   3.695%   $96.6956   $96.70   $96.70   $96.70  
  Purchase #7 $65.92   7.315%   $70.742   $70.74   $70.75   $70.70  
  7 purchase totals = $1,004.41       $1,095.4269   $1,095.43   $1,095.40   $1,095.40