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	$58.48	12.551%	$65.8198	$65.82	$65.80	$65.80
Purchase #2	$131.26	12.709%	$147.9418	$147.94	$147.95	$147.90
Purchase #3	$90.58	7.530%	$97.4007	$97.40	$97.40	$97.40
Purchase #4	$31.32	5.570%	$33.0645	$33.06	$33.05	$33.10
Purchase #5	$129.77	10.591%	$143.5139	$143.51	$143.50	$143.50
Purchase #6	$233.95	12.703%	$263.6687	$263.67	$263.65	$263.70
Purchase #7	$158.74	13.327%	$179.8953	$179.90	$179.90	$179.90
7 purchase totals =	$834.10		$931.3047	$931.30	$931.25	$931.30