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 $54.46   10.471%   $60.1625   $60.16   $60.15   $60.20  
  Purchase #2 $225.48   4.528%   $235.6897   $235.69   $235.70   $235.70  
  Purchase #3 $113.98   11.297%   $126.8563   $126.86   $126.85   $126.90  
  Purchase #4 $209.64   10.149%   $230.9164   $230.92   $230.90   $230.90  
  Purchase #5 $64.44   7.744%   $69.4302   $69.43   $69.45   $69.40  
  Purchase #6 $233.80   13.209%   $264.6826   $264.68   $264.70   $264.70  
  Purchase #7 $242.86   4.639%   $254.1263   $254.13   $254.15   $254.10  
  7 purchase totals = $1,144.66       $1,241.8640   $1,241.87   $1,241.90   $1,241.90