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 $234.73   7.762%   $252.9497   $252.95   $252.95   $252.90  
  Purchase #2 $188.57   10.647%   $208.647   $208.65   $208.65   $208.60  
  Purchase #3 $69.50   7.599%   $74.7813   $74.78   $74.80   $74.80  
  Purchase #4 $202.94   3.639%   $210.325   $210.33   $210.35   $210.30  
  Purchase #5 $180.70   6.745%   $192.8882   $192.89   $192.90   $192.90  
  Purchase #6 $111.71   11.595%   $124.6628   $124.66   $124.65   $124.70  
  Purchase #7 $92.41   10.277%   $101.907   $101.91   $101.90   $101.90  
  7 purchase totals = $1,080.56       $1,166.1610   $1,166.17   $1,166.20   $1,166.10