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	$238.60	13.306%	$270.3481	$270.35	$270.35	$270.30
Purchase #2	$223.28	8.722%	$242.7545	$242.75	$242.75	$242.80
Purchase #3	$53.80	10.771%	$59.5948	$59.59	$59.60	$59.60
Purchase #4	$28.81	10.503%	$31.8359	$31.84	$31.85	$31.80
Purchase #5	$199.51	11.564%	$222.5813	$222.58	$222.60	$222.60
Purchase #6	$86.39	3.153%	$89.1139	$89.11	$89.10	$89.10
Purchase #7	$243.95	13.599%	$277.1248	$277.12	$277.10	$277.10
7 purchase totals =	$1,074.34		$1,193.3533	$1,193.34	$1,193.35	$1,193.30