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	$40.68	6.113%	$43.1668	$43.17	$43.15	$43.20
Purchase #2	$188.48	4.125%	$196.2548	$196.25	$196.25	$196.30
Purchase #3	$110.98	5.191%	$116.741	$116.74	$116.75	$116.70
Purchase #4	$64.46	11.563%	$71.9135	$71.91	$71.90	$71.90
Purchase #5	$30.85	4.234%	$32.1562	$32.16	$32.15	$32.20
Purchase #6	$63.34	3.182%	$65.3555	$65.36	$65.35	$65.40
Purchase #7	$29.37	5.854%	$31.0893	$31.09	$31.10	$31.10
7 purchase totals =	$528.16		$556.6771	$556.68	$556.65	$556.80