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 $23.66   13.817%   $26.9291   $26.93   $26.95   $26.90  
  Purchase #2 $34.82   6.742%   $37.1676   $37.17   $37.15   $37.20  
  Purchase #3 $217.92   6.805%   $232.7495   $232.75   $232.75   $232.70  
  Purchase #4 $248.51   4.541%   $259.7948   $259.79   $259.80   $259.80  
  Purchase #5 $92.94   12.795%   $104.8317   $104.83   $104.85   $104.80  
  Purchase #6 $63.93   4.563%   $66.8471   $66.85   $66.85   $66.80  
  Purchase #7 $16.55   11.154%   $18.396   $18.40   $18.40   $18.40  
  7 purchase totals = $698.33       $746.7158   $746.72   $746.75   $746.60