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	$188.61	12.345%	$211.8939	$211.89	$211.90	$211.90
Purchase #2	$34.58	5.691%	$36.5479	$36.55	$36.55	$36.50
Purchase #3	$124.92	4.755%	$130.8599	$130.86	$130.85	$130.90
Purchase #4	$100.52	13.319%	$113.9083	$113.91	$113.90	$113.90
Purchase #5	$78.60	5.304%	$82.7689	$82.77	$82.75	$82.80
Purchase #6	$52.38	6.294%	$55.6768	$55.68	$55.70	$55.70
Purchase #7	$58.44	4.686%	$61.1785	$61.18	$61.20	$61.20
7 purchase totals =	$638.05		$692.8342	$692.84	$692.85	$692.90