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	$222.33	6.448%	$236.6658	$236.67	$236.65	$236.70
Purchase #2	$247.97	12.127%	$278.0413	$278.04	$278.05	$278.00
Purchase #3	$241.59	4.727%	$253.01	$253.01	$253.00	$253.00
Purchase #4	$25.90	9.158%	$28.2719	$28.27	$28.25	$28.30
Purchase #5	$11.77	7.320%	$12.6316	$12.63	$12.65	$12.60
Purchase #6	$98.89	6.225%	$105.0459	$105.05	$105.05	$105.00
Purchase #7	$62.90	3.814%	$65.299	$65.30	$65.30	$65.30
7 purchase totals =	$911.35		$978.9655	$978.97	$978.95	$978.90