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	$123.33	8.173%	$133.4098	$133.41	$133.40	$133.40
Purchase #2	$142.38	5.453%	$150.144	$150.14	$150.15	$150.10
Purchase #3	$84.53	4.692%	$88.4961	$88.50	$88.50	$88.50
Purchase #4	$223.80	4.301%	$233.4256	$233.43	$233.45	$233.40
Purchase #5	$20.88	11.110%	$23.1998	$23.20	$23.20	$23.20
Purchase #6	$226.37	7.240%	$242.7592	$242.76	$242.75	$242.80
Purchase #7	$61.54	9.484%	$67.3765	$67.38	$67.40	$67.40
7 purchase totals =	$882.83		$938.8110	$938.82	$938.85	$938.80