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	$158.90	5.685%	$167.9335	$167.93	$167.95	$167.90
Purchase #2	$223.63	7.461%	$240.315	$240.32	$240.30	$240.30
Purchase #3	$245.43	7.344%	$263.4544	$263.45	$263.45	$263.50
Purchase #4	$50.78	12.673%	$57.2153	$57.22	$57.20	$57.20
Purchase #5	$65.51	10.746%	$72.5497	$72.55	$72.55	$72.50
Purchase #6	$75.89	8.771%	$82.5463	$82.55	$82.55	$82.50
Purchase #7	$6.75	6.467%	$7.1865	$7.19	$7.20	$7.20
7 purchase totals =	$826.89		$891.2007	$891.21	$891.20	$891.10