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 $233.25   8.301%   $252.6121   $252.61   $252.60   $252.60  
  Purchase #2 $57.43   12.560%   $64.6432   $64.64   $64.65   $64.60  
  Purchase #3 $211.85   5.859%   $224.2623   $224.26   $224.25   $224.30  
  Purchase #4 $184.78   5.379%   $194.7193   $194.72   $194.70   $194.70  
  Purchase #5 $62.88   7.158%   $67.381   $67.38   $67.40   $67.40  
  Purchase #6 $25.25   5.446%   $26.6251   $26.63   $26.65   $26.60  
  Purchase #7 $224.27   12.551%   $252.4181   $252.42   $252.40   $252.40  
  7 purchase totals = $999.71       $1,082.6611   $1,082.66   $1,082.65   $1,082.60