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 $202.39   3.145%   $208.7552   $208.76   $208.75   $208.80  
  Purchase #2 $241.63   12.866%   $272.7181   $272.72   $272.70   $272.70  
  Purchase #3 $144.80   5.696%   $153.0478   $153.05   $153.05   $153.00  
  Purchase #4 $120.55   12.192%   $135.2475   $135.25   $135.25   $135.20  
  Purchase #5 $159.51   4.811%   $167.184   $167.18   $167.20   $167.20  
  Purchase #6 $243.26   12.612%   $273.94   $273.94   $273.95   $273.90  
  Purchase #7 $50.82   8.150%   $54.9618   $54.96   $54.95   $55.00  
  7 purchase totals = $1,162.96       $1,265.8544   $1,265.86   $1,265.85   $1,265.80