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 $246.66   11.741%   $275.6204   $275.62   $275.60   $275.60  
  Purchase #2 $171.88   12.246%   $192.9284   $192.93   $192.95   $192.90  
  Purchase #3 $45.51   5.511%   $48.0181   $48.02   $48.00   $48.00  
  Purchase #4 $171.85   9.508%   $188.1895   $188.19   $188.20   $188.20  
  Purchase #5 $64.99   13.215%   $73.5784   $73.58   $73.60   $73.60  
  Purchase #6 $195.70   10.692%   $216.6242   $216.62   $216.60   $216.60  
  Purchase #7 $170.32   10.455%   $188.127   $188.13   $188.15   $188.10  
  7 purchase totals = $1,066.91       $1,183.0860   $1,183.09   $1,183.10   $1,183.00