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	$142.44	11.838%	$159.302	$159.30	$159.30	$159.30
Purchase #2	$80.48	13.536%	$91.3738	$91.37	$91.35	$91.40
Purchase #3	$135.51	12.271%	$152.1384	$152.14	$152.15	$152.10
Purchase #4	$72.78	12.612%	$81.959	$81.96	$81.95	$82.00
Purchase #5	$53.54	11.545%	$59.7212	$59.72	$59.70	$59.70
Purchase #6	$82.49	7.241%	$88.4631	$88.46	$88.45	$88.50
Purchase #7	$33.89	12.520%	$38.133	$38.13	$38.15	$38.10
7 purchase totals =	$601.13		$671.0905	$671.08	$671.05	$671.10