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	$223.94	4.371%	$233.7284	$233.73	$233.75	$233.70
Purchase #2	$29.55	12.329%	$33.1932	$33.19	$33.20	$33.20
Purchase #3	$128.31	9.804%	$140.8895	$140.89	$140.90	$140.90
Purchase #4	$209.87	3.570%	$217.3624	$217.36	$217.35	$217.40
Purchase #5	$102.49	3.488%	$106.0649	$106.06	$106.05	$106.10
Purchase #6	$109.78	9.606%	$120.3255	$120.33	$120.35	$120.30
Purchase #7	$112.74	12.853%	$127.2305	$127.23	$127.25	$127.20
7 purchase totals =	$916.68		$978.7944	$978.79	$978.85	$978.80