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	$202.48	3.168%	$208.8946	$208.89	$208.90	$208.90
Purchase #2	$13.60	13.498%	$15.4357	$15.44	$15.45	$15.40
Purchase #3	$18.28	10.333%	$20.1689	$20.17	$20.15	$20.20
Purchase #4	$22.50	13.532%	$25.5447	$25.54	$25.55	$25.50
Purchase #5	$163.47	9.354%	$178.761	$178.76	$178.75	$178.80
Purchase #6	$33.57	12.568%	$37.7891	$37.79	$37.80	$37.80
Purchase #7	$27.56	4.799%	$28.8826	$28.88	$28.90	$28.90
7 purchase totals =	$481.46		$515.4766	$515.47	$515.50	$515.50