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	$170.96	10.463%	$188.8475	$188.85	$188.85	$188.80
Purchase #2	$73.56	9.104%	$80.2569	$80.26	$80.25	$80.30
Purchase #3	$170.59	5.268%	$179.5767	$179.58	$179.60	$179.60
Purchase #4	$86.89	4.676%	$90.953	$90.95	$90.95	$91.00
Purchase #5	$120.97	13.148%	$136.8751	$136.88	$136.90	$136.90
Purchase #6	$136.99	10.759%	$151.7288	$151.73	$151.75	$151.70
Purchase #7	$140.44	9.271%	$153.4602	$153.46	$153.45	$153.50
7 purchase totals =	$900.40		$981.6982	$981.71	$981.75	$981.80