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 $36.92   4.703%   $38.6563   $38.66   $38.65   $38.70  
  Purchase #2 $101.46   3.690%   $105.2039   $105.20   $105.20   $105.20  
  Purchase #3 $183.93   6.436%   $195.7677   $195.77   $195.75   $195.80  
  Purchase #4 $247.53   10.486%   $273.486   $273.49   $273.50   $273.50  
  Purchase #5 $183.41   6.853%   $195.9791   $195.98   $196.00   $196.00  
  Purchase #6 $210.69   3.231%   $217.4974   $217.50   $217.50   $217.50  
  Purchase #7 $159.63   4.216%   $166.36   $166.36   $166.35   $166.40  
  7 purchase totals = $1,123.57       $1,192.9504   $1,192.96   $1,192.95   $1,193.10