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	$99.55	10.205%	$109.7091	$109.71	$109.70	$109.70
Purchase #2	$83.94	6.831%	$89.6739	$89.67	$89.65	$89.70
Purchase #3	$165.59	5.417%	$174.56	$174.56	$174.55	$174.60
Purchase #4	$142.64	5.317%	$150.2242	$150.22	$150.20	$150.20
Purchase #5	$50.50	8.457%	$54.7708	$54.77	$54.75	$54.80
Purchase #6	$185.51	9.240%	$202.6511	$202.65	$202.65	$202.70
Purchase #7	$7.50	9.621%	$8.2216	$8.22	$8.20	$8.20
7 purchase totals =	$735.23		$789.8107	$789.80	$789.70	$789.90