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	$37.25	7.808%	$40.1585	$40.16	$40.15	$40.20
Purchase #2	$50.72	9.547%	$55.5622	$55.56	$55.55	$55.60
Purchase #3	$5.33	13.726%	$6.0616	$6.06	$6.05	$6.10
Purchase #4	$218.96	10.606%	$242.1829	$242.18	$242.20	$242.20
Purchase #5	$223.69	6.534%	$238.3059	$238.31	$238.30	$238.30
Purchase #6	$61.51	9.857%	$67.573	$67.57	$67.55	$67.60
Purchase #7	$170.28	8.256%	$184.3383	$184.34	$184.35	$184.30
7 purchase totals =	$767.74		$834.1824	$834.18	$834.15	$834.30