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	$121.70	5.567%	$128.475	$128.48	$128.50	$128.50
Purchase #2	$142.74	3.872%	$148.2669	$148.27	$148.25	$148.30
Purchase #3	$32.34	6.769%	$34.5291	$34.53	$34.55	$34.50
Purchase #4	$32.26	13.367%	$36.5722	$36.57	$36.55	$36.60
Purchase #5	$35.27	12.126%	$39.5468	$39.55	$39.55	$39.50
Purchase #6	$52.37	5.337%	$55.165	$55.17	$55.15	$55.20
Purchase #7	$145.64	13.626%	$165.4849	$165.48	$165.50	$165.50
7 purchase totals =	$562.32		$608.0399	$608.05	$608.05	$608.10