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	$11.47	5.329%	$12.0812	$12.08	$12.10	$12.10
Purchase #2	$170.65	6.839%	$182.3208	$182.32	$182.30	$182.30
Purchase #3	$130.96	4.855%	$137.3181	$137.32	$137.30	$137.30
Purchase #4	$88.95	12.695%	$100.2422	$100.24	$100.25	$100.20
Purchase #5	$125.28	12.732%	$141.2306	$141.23	$141.25	$141.20
Purchase #6	$110.91	6.751%	$118.3975	$118.40	$118.40	$118.40
Purchase #7	$125.72	10.643%	$139.1004	$139.10	$139.10	$139.10
7 purchase totals =	$763.94		$830.6908	$830.69	$830.70	$830.60