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	$89.69	4.362%	$93.6023	$93.60	$93.60	$93.60
Purchase #2	$81.72	4.344%	$85.2699	$85.27	$85.25	$85.30
Purchase #3	$80.43	9.864%	$88.3636	$88.36	$88.35	$88.40
Purchase #4	$23.92	10.688%	$26.4766	$26.48	$26.50	$26.50
Purchase #5	$78.36	13.784%	$89.1611	$89.16	$89.15	$89.20
Purchase #6	$80.63	10.424%	$89.0349	$89.03	$89.05	$89.00
Purchase #7	$54.34	5.314%	$57.2276	$57.23	$57.25	$57.20
7 purchase totals =	$489.09		$529.1360	$529.13	$529.15	$529.20