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	$67.92	4.853%	$71.2162	$71.22	$71.20	$71.20
Purchase #2	$64.40	4.860%	$67.5298	$67.53	$67.55	$67.50
Purchase #3	$223.66	12.342%	$251.2641	$251.26	$251.25	$251.30
Purchase #4	$76.50	8.563%	$83.0507	$83.05	$83.05	$83.10
Purchase #5	$31.66	9.778%	$34.7557	$34.76	$34.75	$34.80
Purchase #6	$45.75	3.479%	$47.3416	$47.34	$47.35	$47.30
Purchase #7	$40.28	7.838%	$43.4371	$43.44	$43.45	$43.40
7 purchase totals =	$550.17		$598.5952	$598.60	$598.60	$598.60