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	$206.29	3.204%	$212.8995	$212.90	$212.90	$212.90
Purchase #2	$223.89	10.150%	$246.6148	$246.61	$246.60	$246.60
Purchase #3	$94.82	7.833%	$102.2473	$102.25	$102.25	$102.20
Purchase #4	$72.58	8.717%	$78.9068	$78.91	$78.90	$78.90
Purchase #5	$34.76	3.650%	$36.0287	$36.03	$36.05	$36.00
Purchase #6	$6.91	13.635%	$7.8522	$7.85	$7.85	$7.90
Purchase #7	$146.73	12.585%	$165.196	$165.20	$165.20	$165.20
7 purchase totals =	$785.98		$849.7453	$849.75	$849.75	$849.70