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	$134.78	8.751%	$146.5746	$146.57	$146.55	$146.60
Purchase #2	$223.77	13.114%	$253.1152	$253.12	$253.10	$253.10
Purchase #3	$174.60	5.259%	$183.7822	$183.78	$183.80	$183.80
Purchase #4	$137.39	3.655%	$142.4116	$142.41	$142.40	$142.40
Purchase #5	$186.27	6.785%	$198.9084	$198.91	$198.90	$198.90
Purchase #6	$215.49	3.635%	$223.3231	$223.32	$223.30	$223.30
Purchase #7	$59.36	9.661%	$65.0948	$65.09	$65.10	$65.10
7 purchase totals =	$1,131.66		$1,213.2099	$1,213.20	$1,213.15	$1,213.20