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 $159.61   10.134%   $175.7849   $175.78   $175.80   $175.80  
  Purchase #2 $185.29   9.402%   $202.711   $202.71   $202.70   $202.70  
  Purchase #3 $79.78   10.548%   $88.1952   $88.20   $88.20   $88.20  
  Purchase #4 $235.57   11.763%   $263.2801   $263.28   $263.30   $263.30  
  Purchase #5 $63.97   3.225%   $66.033   $66.03   $66.05   $66.00  
  Purchase #6 $48.57   4.859%   $50.93   $50.93   $50.95   $50.90  
  Purchase #7 $233.68   11.262%   $259.997   $260.00   $260.00   $260.00  
  7 purchase totals = $1,006.47       $1,106.9312   $1,106.93   $1,107.00   $1,106.90