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 $88.69   3.776%   $92.0389   $92.04   $92.05   $92.00  
  Purchase #2 $34.55   11.797%   $38.6259   $38.63   $38.65   $38.60  
  Purchase #3 $220.65   8.480%   $239.3611   $239.36   $239.35   $239.40  
  Purchase #4 $95.91   13.293%   $108.6593   $108.66   $108.65   $108.70  
  Purchase #5 $152.59   3.447%   $157.8498   $157.85   $157.85   $157.80  
  Purchase #6 $248.94   7.143%   $266.7218   $266.72   $266.70   $266.70  
  Purchase #7 $114.79   4.293%   $119.7179   $119.72   $119.70   $119.70  
  7 purchase totals = $956.12       $1,022.9747   $1,022.98   $1,022.95   $1,022.90