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	$198.29	12.616%	$223.3063	$223.31	$223.30	$223.30
Purchase #2	$133.40	12.829%	$150.5139	$150.51	$150.50	$150.50
Purchase #3	$174.52	10.339%	$192.5636	$192.56	$192.55	$192.60
Purchase #4	$110.95	4.275%	$115.6931	$115.69	$115.70	$115.70
Purchase #5	$67.69	5.614%	$71.4901	$71.49	$71.50	$71.50
Purchase #6	$35.45	9.140%	$38.6901	$38.69	$38.70	$38.70
Purchase #7	$45.97	8.827%	$50.0278	$50.03	$50.05	$50.00
7 purchase totals =	$766.27		$842.2849	$842.28	$842.30	$842.30