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	$159.30	7.547%	$171.3224	$171.32	$171.30	$171.30
Purchase #2	$31.54	10.526%	$34.8599	$34.86	$34.85	$34.90
Purchase #3	$169.34	9.654%	$185.6881	$185.69	$185.70	$185.70
Purchase #4	$109.35	13.362%	$123.9613	$123.96	$123.95	$124.00
Purchase #5	$93.36	4.683%	$97.732	$97.73	$97.75	$97.70
Purchase #6	$153.89	8.832%	$167.4816	$167.48	$167.50	$167.50
Purchase #7	$17.54	6.422%	$18.6664	$18.67	$18.65	$18.70
7 purchase totals =	$734.32		$799.7117	$799.71	$799.70	$799.80