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 $93.65   3.537%   $96.9624   $96.96   $96.95   $97.00  
  Purchase #2 $19.31   9.675%   $21.1782   $21.18   $21.20   $21.20  
  Purchase #3 $163.42   12.254%   $183.4455   $183.45   $183.45   $183.40  
  Purchase #4 $244.79   5.743%   $258.8483   $258.85   $258.85   $258.80  
  Purchase #5 $39.54   11.609%   $44.1302   $44.13   $44.15   $44.10  
  Purchase #6 $76.27   8.394%   $82.6721   $82.67   $82.65   $82.70  
  Purchase #7 $239.79   3.608%   $248.4416   $248.44   $248.45   $248.40  
  7 purchase totals = $876.77       $935.6783   $935.68   $935.70   $935.60