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 $162.58   6.146%   $172.5722   $172.57   $172.55   $172.60  
  Purchase #2 $121.47   3.452%   $125.6631   $125.66   $125.65   $125.70  
  Purchase #3 $249.83   5.486%   $263.5357   $263.54   $263.55   $263.50  
  Purchase #4 $206.78   8.452%   $224.257   $224.26   $224.25   $224.30  
  Purchase #5 $202.91   6.729%   $216.5638   $216.56   $216.55   $216.60  
  Purchase #6 $188.47   4.779%   $197.477   $197.48   $197.50   $197.50  
  Purchase #7 $62.99   12.776%   $71.0376   $71.04   $71.05   $71.00  
  7 purchase totals = $1,195.03       $1,271.1064   $1,271.11   $1,271.10   $1,271.20