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	$137.81	12.537%	$155.0872	$155.09	$155.10	$155.10
Purchase #2	$218.99	11.656%	$244.5155	$244.52	$244.50	$244.50
Purchase #3	$154.40	8.630%	$167.7247	$167.72	$167.70	$167.70
Purchase #4	$48.61	12.644%	$54.7562	$54.76	$54.75	$54.80
Purchase #5	$178.57	7.389%	$191.7645	$191.76	$191.75	$191.80
Purchase #6	$29.36	10.408%	$32.4158	$32.42	$32.40	$32.40
Purchase #7	$216.85	12.452%	$243.8522	$243.85	$243.85	$243.90
7 purchase totals =	$984.59		$1,090.1161	$1,090.12	$1,090.05	$1,090.20