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 $239.38   10.786%   $265.1995   $265.20   $265.20   $265.20  
  Purchase #2 $32.76   3.582%   $33.9335   $33.93   $33.95   $33.90  
  Purchase #3 $205.64   10.328%   $226.8785   $226.88   $226.90   $226.90  
  Purchase #4 $244.28   10.439%   $269.7804   $269.78   $269.80   $269.80  
  Purchase #5 $133.26   12.721%   $150.212   $150.21   $150.20   $150.20  
  Purchase #6 $61.49   12.873%   $69.4056   $69.41   $69.40   $69.40  
  Purchase #7 $157.74   9.532%   $172.7758   $172.78   $172.80   $172.80  
  7 purchase totals = $1,074.55       $1,188.1853   $1,188.19   $1,188.25   $1,188.20