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 $24.93   3.477%   $25.7968   $25.80   $25.80   $25.80  
  Purchase #2 $228.95   5.707%   $242.0162   $242.02   $242.00   $242.00  
  Purchase #3 $194.31   6.427%   $206.7983   $206.80   $206.80   $206.80  
  Purchase #4 $50.33   7.390%   $54.0494   $54.05   $54.05   $54.00  
  Purchase #5 $47.86   10.167%   $52.7259   $52.73   $52.75   $52.70  
  Purchase #6 $207.94   3.351%   $214.9081   $214.91   $214.90   $214.90  
  Purchase #7 $58.31   7.158%   $62.4838   $62.48   $62.50   $62.50  
  7 purchase totals = $812.63       $858.7785   $858.79   $858.80   $858.70