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	$80.57	3.769%	$83.6067	$83.61	$83.60	$83.60
Purchase #2	$210.35	8.428%	$228.0783	$228.08	$228.10	$228.10
Purchase #3	$54.89	13.451%	$62.2733	$62.27	$62.25	$62.30
Purchase #4	$168.91	9.836%	$185.524	$185.52	$185.50	$185.50
Purchase #5	$34.85	8.698%	$37.8813	$37.88	$37.90	$37.90
Purchase #6	$31.87	13.389%	$36.1371	$36.14	$36.15	$36.10
Purchase #7	$247.46	8.588%	$268.7119	$268.71	$268.70	$268.70
7 purchase totals =	$828.90		$902.2126	$902.21	$902.20	$902.20