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 $210.82   7.601%   $226.8444   $226.84   $226.85   $226.80  
  Purchase #2 $232.83   13.683%   $264.6881   $264.69   $264.70   $264.70  
  Purchase #3 $165.27   8.734%   $179.7047   $179.70   $179.70   $179.70  
  Purchase #4 $248.29   8.166%   $268.5654   $268.57   $268.55   $268.60  
  Purchase #5 $202.73   11.557%   $226.1595   $226.16   $226.15   $226.20  
  Purchase #6 $121.67   13.821%   $138.486   $138.49   $138.50   $138.50  
  Purchase #7 $195.75   6.440%   $208.3563   $208.36   $208.35   $208.40  
  7 purchase totals = $1,377.36       $1,512.8044   $1,512.81   $1,512.80   $1,512.90