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	$19.48	10.170%	$21.4611	$21.46	$21.45	$21.50
Purchase #2	$168.76	5.565%	$178.1515	$178.15	$178.15	$178.20
Purchase #3	$209.39	7.162%	$224.3865	$224.39	$224.40	$224.40
Purchase #4	$226.51	5.278%	$238.4652	$238.47	$238.45	$238.50
Purchase #5	$23.63	7.660%	$25.4401	$25.44	$25.45	$25.40
Purchase #6	$72.82	6.720%	$77.7135	$77.71	$77.70	$77.70
Purchase #7	$214.32	11.117%	$238.146	$238.15	$238.15	$238.10
7 purchase totals =	$934.91		$1,003.7639	$1,003.77	$1,003.75	$1,003.80