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	$119.26	8.114%	$128.9368	$128.94	$128.95	$128.90
Purchase #2	$65.50	7.120%	$70.1636	$70.16	$70.15	$70.20
Purchase #3	$80.63	12.574%	$90.7684	$90.77	$90.75	$90.80
Purchase #4	$72.29	8.122%	$78.1614	$78.16	$78.15	$78.20
Purchase #5	$119.39	3.226%	$123.2415	$123.24	$123.25	$123.20
Purchase #6	$85.41	13.290%	$96.761	$96.76	$96.75	$96.80
Purchase #7	$55.38	4.186%	$57.6982	$57.70	$57.70	$57.70
7 purchase totals =	$597.86		$645.7309	$645.73	$645.70	$645.80