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 $174.33   11.697%   $194.7214   $194.72   $194.70   $194.70  
  Purchase #2 $60.82   10.149%   $66.9926   $66.99   $67.00   $67.00  
  Purchase #3 $61.76   5.648%   $65.2482   $65.25   $65.25   $65.20  
  Purchase #4 $158.44   10.468%   $175.0255   $175.03   $175.05   $175.00  
  Purchase #5 $176.31   4.807%   $184.7852   $184.79   $184.80   $184.80  
  Purchase #6 $177.73   3.643%   $184.2047   $184.20   $184.20   $184.20  
  Purchase #7 $115.67   13.478%   $131.26   $131.26   $131.25   $131.30  
  7 purchase totals = $925.06       $1,002.2376   $1,002.24   $1,002.25   $1,002.20