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 $54.96   7.669%   $59.1749   $59.17   $59.15   $59.20  
  Purchase #2 $69.51   9.310%   $75.9814   $75.98   $76.00   $76.00  
  Purchase #3 $129.47   3.411%   $133.8862   $133.89   $133.90   $133.90  
  Purchase #4 $166.48   3.561%   $172.4084   $172.41   $172.40   $172.40  
  Purchase #5 $220.92   10.125%   $243.2882   $243.29   $243.30   $243.30  
  Purchase #6 $183.28   8.312%   $198.5142   $198.51   $198.50   $198.50  
  Purchase #7 $30.74   8.764%   $33.4341   $33.43   $33.45   $33.40  
  7 purchase totals = $855.36       $916.6874   $916.68   $916.70   $916.70