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	$48.35	3.322%	$49.9562	$49.96	$49.95	$50.00
Purchase #2	$81.43	10.125%	$89.6748	$89.67	$89.65	$89.70
Purchase #3	$134.62	11.759%	$150.45	$150.45	$150.45	$150.50
Purchase #4	$110.27	11.672%	$123.1407	$123.14	$123.15	$123.10
Purchase #5	$28.27	6.534%	$30.1172	$30.12	$30.10	$30.10
Purchase #6	$224.69	11.539%	$250.617	$250.62	$250.60	$250.60
Purchase #7	$85.56	11.408%	$95.3207	$95.32	$95.30	$95.30
7 purchase totals =	$713.19		$789.2766	$789.28	$789.20	$789.30