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 $249.53   11.236%   $277.5672   $277.57   $277.55   $277.60  
  Purchase #2 $225.42   9.551%   $246.9499   $246.95   $246.95   $246.90  
  Purchase #3 $19.42   5.595%   $20.5065   $20.51   $20.50   $20.50  
  Purchase #4 $203.43   11.214%   $226.2426   $226.24   $226.25   $226.20  
  Purchase #5 $182.27   5.439%   $192.1837   $192.18   $192.20   $192.20  
  Purchase #6 $235.93   3.482%   $244.1451   $244.15   $244.15   $244.10  
  Purchase #7 $105.80   9.629%   $115.9875   $115.99   $116.00   $116.00  
  7 purchase totals = $1,221.80       $1,323.5825   $1,323.59   $1,323.60   $1,323.50