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	$121.79	5.731%	$128.7698	$128.77	$128.75	$128.80
Purchase #2	$60.87	10.463%	$67.2388	$67.24	$67.25	$67.20
Purchase #3	$26.52	13.561%	$30.1164	$30.12	$30.10	$30.10
Purchase #4	$114.96	7.136%	$123.1635	$123.16	$123.15	$123.20
Purchase #5	$188.72	4.127%	$196.5085	$196.51	$196.50	$196.50
Purchase #6	$190.80	5.413%	$201.128	$201.13	$201.15	$201.10
Purchase #7	$136.84	11.637%	$152.7641	$152.76	$152.75	$152.80
7 purchase totals =	$840.50		$899.6891	$899.69	$899.65	$899.70