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	$166.68	3.739%	$172.9122	$172.91	$172.90	$172.90
Purchase #2	$31.53	3.280%	$32.5642	$32.56	$32.55	$32.60
Purchase #3	$94.44	6.440%	$100.5219	$100.52	$100.50	$100.50
Purchase #4	$13.31	6.355%	$14.1559	$14.16	$14.15	$14.20
Purchase #5	$53.64	12.759%	$60.4839	$60.48	$60.50	$60.50
Purchase #6	$157.48	4.605%	$164.732	$164.73	$164.75	$164.70
Purchase #7	$8.62	10.470%	$9.5225	$9.52	$9.50	$9.50
7 purchase totals =	$525.70		$554.8926	$554.88	$554.85	$554.90