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	$47.38	7.132%	$50.7591	$50.76	$50.75	$50.80
Purchase #2	$164.75	10.817%	$182.571	$182.57	$182.55	$182.60
Purchase #3	$59.66	7.747%	$64.2819	$64.28	$64.30	$64.30
Purchase #4	$64.45	3.282%	$66.5652	$66.57	$66.55	$66.60
Purchase #5	$238.31	13.643%	$270.8226	$270.82	$270.80	$270.80
Purchase #6	$149.94	10.396%	$165.5278	$165.53	$165.55	$165.50
Purchase #7	$162.39	10.834%	$179.9833	$179.98	$180.00	$180.00
7 purchase totals =	$886.88		$980.5109	$980.51	$980.50	$980.60