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	$6.36	12.608%	$7.1619	$7.16	$7.15	$7.20
Purchase #2	$109.42	10.273%	$120.6607	$120.66	$120.65	$120.70
Purchase #3	$18.66	10.113%	$20.5471	$20.55	$20.55	$20.50
Purchase #4	$182.91	4.782%	$191.6568	$191.66	$191.65	$191.70
Purchase #5	$174.83	12.636%	$196.9215	$196.92	$196.90	$196.90
Purchase #6	$146.71	7.693%	$157.9964	$158.00	$158.00	$158.00
Purchase #7	$196.26	13.233%	$222.2311	$222.23	$222.25	$222.20
7 purchase totals =	$835.15		$917.1755	$917.18	$917.15	$917.20