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 $160.73   8.291%   $174.0561   $174.06   $174.05   $174.10  
  Purchase #2 $116.26   9.203%   $126.9594   $126.96   $126.95   $127.00  
  Purchase #3 $49.81   3.286%   $51.4468   $51.45   $51.45   $51.40  
  Purchase #4 $182.89   5.545%   $193.0313   $193.03   $193.05   $193.00  
  Purchase #5 $69.73   5.267%   $73.4027   $73.40   $73.40   $73.40  
  Purchase #6 $219.96   8.787%   $239.2879   $239.29   $239.30   $239.30  
  Purchase #7 $85.36   9.413%   $93.3949   $93.39   $93.40   $93.40  
  7 purchase totals = $884.74       $951.5791   $951.58   $951.60   $951.60