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	$136.75	11.836%	$152.9357	$152.94	$152.95	$152.90
Purchase #2	$59.87	9.371%	$65.4804	$65.48	$65.50	$65.50
Purchase #3	$59.57	5.487%	$62.8386	$62.84	$62.85	$62.80
Purchase #4	$63.92	4.167%	$66.5835	$66.58	$66.60	$66.60
Purchase #5	$22.60	11.392%	$25.1746	$25.17	$25.15	$25.20
Purchase #6	$28.33	4.562%	$29.6224	$29.62	$29.60	$29.60
Purchase #7	$104.61	5.554%	$110.42	$110.42	$110.40	$110.40
7 purchase totals =	$475.65		$513.0552	$513.05	$513.05	$513.00