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 $54.74   13.293%   $62.0166   $62.02   $62.00   $62.00  
  Purchase #2 $103.70   12.521%   $116.6843   $116.68   $116.70   $116.70  
  Purchase #3 $127.45   11.163%   $141.6772   $141.68   $141.70   $141.70  
  Purchase #4 $117.77   7.706%   $126.8454   $126.85   $126.85   $126.80  
  Purchase #5 $162.89   13.369%   $184.6668   $184.67   $184.65   $184.70  
  Purchase #6 $20.97   10.469%   $23.1653   $23.17   $23.15   $23.20  
  Purchase #7 $153.25   10.231%   $168.929   $168.93   $168.95   $168.90  
  7 purchase totals = $740.77       $823.9846   $824.00   $824.00   $824.00