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	$133.31	3.549%	$138.0412	$138.04	$138.05	$138.00
Purchase #2	$222.72	12.562%	$250.6981	$250.70	$250.70	$250.70
Purchase #3	$26.60	10.396%	$29.3653	$29.37	$29.35	$29.40
Purchase #4	$203.84	6.413%	$216.9123	$216.91	$216.90	$216.90
Purchase #5	$189.92	3.506%	$196.5786	$196.58	$196.60	$196.60
Purchase #6	$48.76	9.107%	$53.2006	$53.20	$53.20	$53.20
Purchase #7	$50.66	10.328%	$55.8922	$55.89	$55.90	$55.90
7 purchase totals =	$875.81		$940.6883	$940.69	$940.70	$940.70