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 $230.93   5.834%   $244.4025   $244.40   $244.40   $244.40  
  Purchase #2 $167.58   7.117%   $179.5067   $179.51   $179.50   $179.50  
  Purchase #3 $34.32   10.833%   $38.0379   $38.04   $38.05   $38.00  
  Purchase #4 $241.78   7.652%   $260.281   $260.28   $260.30   $260.30  
  Purchase #5 $35.25   10.110%   $38.8138   $38.81   $38.80   $38.80  
  Purchase #6 $38.79   11.491%   $43.2474   $43.25   $43.25   $43.20  
  Purchase #7 $245.30   10.220%   $270.3697   $270.37   $270.35   $270.40  
  7 purchase totals = $993.95       $1,074.6590   $1,074.66   $1,074.65   $1,074.60