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 $247.32   5.853%   $261.7956   $261.80   $261.80   $261.80  
  Purchase #2 $232.99   11.700%   $260.2498   $260.25   $260.25   $260.20  
  Purchase #3 $21.96   4.870%   $23.0295   $23.03   $23.05   $23.00  
  Purchase #4 $185.32   4.137%   $192.9867   $192.99   $193.00   $193.00  
  Purchase #5 $43.70   6.694%   $46.6253   $46.63   $46.65   $46.60  
  Purchase #6 $66.55   7.214%   $71.3509   $71.35   $71.35   $71.40  
  Purchase #7 $88.66   7.773%   $95.5515   $95.55   $95.55   $95.60  
  7 purchase totals = $886.50       $951.5893   $951.60   $951.65   $951.60