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	$85.83	12.571%	$96.6197	$96.62	$96.60	$96.60
Purchase #2	$221.48	9.780%	$243.1407	$243.14	$243.15	$243.10
Purchase #3	$103.54	10.128%	$114.0265	$114.03	$114.05	$114.00
Purchase #4	$7.37	13.546%	$8.3683	$8.37	$8.35	$8.40
Purchase #5	$80.50	11.332%	$89.6223	$89.62	$89.60	$89.60
Purchase #6	$201.45	13.289%	$228.2207	$228.22	$228.20	$228.20
Purchase #7	$144.55	4.116%	$150.4997	$150.50	$150.50	$150.50
7 purchase totals =	$844.72		$930.4979	$930.50	$930.45	$930.40