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	$249.34	3.560%	$258.2165	$258.22	$258.20	$258.20
Purchase #2	$13.60	10.506%	$15.0288	$15.03	$15.05	$15.00
Purchase #3	$132.73	13.691%	$150.9021	$150.90	$150.90	$150.90
Purchase #4	$56.60	5.731%	$59.8437	$59.84	$59.85	$59.80
Purchase #5	$232.38	11.448%	$258.9829	$258.98	$259.00	$259.00
Purchase #6	$175.33	5.603%	$185.1537	$185.15	$185.15	$185.20
Purchase #7	$80.81	13.347%	$91.5957	$91.60	$91.60	$91.60
7 purchase totals =	$940.79		$1,019.7234	$1,019.72	$1,019.75	$1,019.70