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 $63.25   5.540%   $66.7541   $66.75   $66.75   $66.80  
  Purchase #2 $228.73   5.687%   $241.7379   $241.74   $241.75   $241.70  
  Purchase #3 $215.57   3.630%   $223.3952   $223.40   $223.40   $223.40  
  Purchase #4 $122.85   6.161%   $130.4188   $130.42   $130.40   $130.40  
  Purchase #5 $146.85   4.799%   $153.8973   $153.90   $153.90   $153.90  
  Purchase #6 $11.97   5.761%   $12.6596   $12.66   $12.65   $12.70  
  Purchase #7 $192.26   10.748%   $212.9241   $212.92   $212.90   $212.90  
  7 purchase totals = $981.48       $1,041.7870   $1,041.79   $1,041.75   $1,041.80