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	$142.41	12.129%	$159.6829	$159.68	$159.70	$159.70
Purchase #2	$31.59	6.617%	$33.6803	$33.68	$33.70	$33.70
Purchase #3	$239.60	13.355%	$271.5986	$271.60	$271.60	$271.60
Purchase #4	$243.62	8.666%	$264.7321	$264.73	$264.75	$264.70
Purchase #5	$226.34	12.872%	$255.4745	$255.47	$255.45	$255.50
Purchase #6	$97.77	12.455%	$109.9473	$109.95	$109.95	$109.90
Purchase #7	$69.95	3.251%	$72.2241	$72.22	$72.20	$72.20
7 purchase totals =	$1,051.28		$1,167.3398	$1,167.33	$1,167.35	$1,167.30