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 $241.67   11.553%   $269.5901   $269.59   $269.60   $269.60  
  Purchase #2 $37.48   9.743%   $41.1317   $41.13   $41.15   $41.10  
  Purchase #3 $188.34   10.696%   $208.4848   $208.48   $208.50   $208.50  
  Purchase #4 $221.85   3.149%   $228.8361   $228.84   $228.85   $228.80  
  Purchase #5 $231.33   10.554%   $255.7446   $255.74   $255.75   $255.70  
  Purchase #6 $189.41   6.599%   $201.9092   $201.91   $201.90   $201.90  
  Purchase #7 $182.32   4.784%   $191.0422   $191.04   $191.05   $191.00  
  7 purchase totals = $1,292.40       $1,396.7387   $1,396.73   $1,396.80   $1,396.60