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	$88.36	12.633%	$99.5225	$99.52	$99.50	$99.50
Purchase #2	$224.78	8.757%	$244.464	$244.46	$244.45	$244.50
Purchase #3	$86.94	10.768%	$96.3017	$96.30	$96.30	$96.30
Purchase #4	$129.40	5.600%	$136.6464	$136.65	$136.65	$136.60
Purchase #5	$113.92	5.780%	$120.5046	$120.50	$120.50	$120.50
Purchase #6	$169.26	8.442%	$183.5489	$183.55	$183.55	$183.50
Purchase #7	$126.51	8.614%	$137.4076	$137.41	$137.40	$137.40
7 purchase totals =	$939.17		$1,018.3957	$1,018.39	$1,018.35	$1,018.30