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	$209.40	3.715%	$217.1792	$217.18	$217.20	$217.20
Purchase #2	$101.47	10.174%	$111.7936	$111.79	$111.80	$111.80
Purchase #3	$39.73	7.327%	$42.641	$42.64	$42.65	$42.60
Purchase #4	$85.75	11.533%	$95.6395	$95.64	$95.65	$95.60
Purchase #5	$148.60	7.826%	$160.2294	$160.23	$160.25	$160.20
Purchase #6	$6.42	3.179%	$6.6241	$6.62	$6.60	$6.60
Purchase #7	$147.28	3.279%	$152.1093	$152.11	$152.10	$152.10
7 purchase totals =	$738.65		$786.2161	$786.21	$786.25	$786.10