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 $193.54   6.439%   $206.002   $206.00   $206.00   $206.00  
  Purchase #2 $191.69   5.560%   $202.348   $202.35   $202.35   $202.30  
  Purchase #3 $157.43   5.143%   $165.5266   $165.53   $165.55   $165.50  
  Purchase #4 $136.82   3.269%   $141.2926   $141.29   $141.30   $141.30  
  Purchase #5 $40.64   11.651%   $45.375   $45.38   $45.40   $45.40  
  Purchase #6 $174.41   10.331%   $192.4283   $192.43   $192.45   $192.40  
  Purchase #7 $225.42   4.804%   $236.2492   $236.25   $236.25   $236.20  
  7 purchase totals = $1,119.95       $1,189.2217   $1,189.23   $1,189.30   $1,189.10