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 $156.26   3.835%   $162.2526   $162.25   $162.25   $162.30  
  Purchase #2 $61.51   13.277%   $69.6767   $69.68   $69.70   $69.70  
  Purchase #3 $244.42   3.412%   $252.7596   $252.76   $252.75   $252.80  
  Purchase #4 $134.47   8.303%   $145.635   $145.64   $145.65   $145.60  
  Purchase #5 $54.79   9.407%   $59.9441   $59.94   $59.95   $59.90  
  Purchase #6 $230.74   12.368%   $259.2779   $259.28   $259.30   $259.30  
  Purchase #7 $246.64   6.342%   $262.2819   $262.28   $262.30   $262.30  
  7 purchase totals = $1,128.83       $1,211.8278   $1,211.83   $1,211.90   $1,211.90