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	$64.44	11.496%	$71.848	$71.85	$71.85	$71.80
Purchase #2	$99.91	11.256%	$111.1559	$111.16	$111.15	$111.20
Purchase #3	$38.70	13.831%	$44.0526	$44.05	$44.05	$44.10
Purchase #4	$27.66	3.764%	$28.7011	$28.70	$28.70	$28.70
Purchase #5	$73.41	12.474%	$82.5672	$82.57	$82.55	$82.60
Purchase #6	$38.72	4.826%	$40.5886	$40.59	$40.60	$40.60
Purchase #7	$38.28	7.510%	$41.1548	$41.15	$41.15	$41.20
7 purchase totals =	$381.12		$420.0682	$420.07	$420.05	$420.20