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	$19.66	3.740%	$20.3953	$20.40	$20.40	$20.40
Purchase #2	$170.46	3.500%	$176.4261	$176.43	$176.45	$176.40
Purchase #3	$106.41	4.213%	$110.8931	$110.89	$110.90	$110.90
Purchase #4	$135.98	10.433%	$150.1668	$150.17	$150.15	$150.20
Purchase #5	$248.69	6.383%	$264.5639	$264.56	$264.55	$264.60
Purchase #6	$207.45	4.231%	$216.2272	$216.23	$216.25	$216.20
Purchase #7	$95.52	4.556%	$99.8719	$99.87	$99.85	$99.90
7 purchase totals =	$984.17		$1,038.5443	$1,038.55	$1,038.55	$1,038.60