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 $33.47   7.541%   $35.994   $35.99   $36.00   $36.00  
  Purchase #2 $183.39   5.116%   $192.7722   $192.77   $192.75   $192.80  
  Purchase #3 $119.98   9.248%   $131.0758   $131.08   $131.10   $131.10  
  Purchase #4 $150.81   10.221%   $166.2243   $166.22   $166.20   $166.20  
  Purchase #5 $44.97   7.575%   $48.3765   $48.38   $48.40   $48.40  
  Purchase #6 $24.40   6.764%   $26.0504   $26.05   $26.05   $26.10  
  Purchase #7 $200.40   8.123%   $216.6785   $216.68   $216.70   $216.70  
  7 purchase totals = $757.42       $817.1717   $817.17   $817.20   $817.30