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	$82.57	9.412%	$90.3415	$90.34	$90.35	$90.30
Purchase #2	$122.78	5.747%	$129.8362	$129.84	$129.85	$129.80
Purchase #3	$53.30	9.695%	$58.4674	$58.47	$58.45	$58.50
Purchase #4	$138.27	3.850%	$143.5934	$143.59	$143.60	$143.60
Purchase #5	$204.37	3.486%	$211.4943	$211.49	$211.50	$211.50
Purchase #6	$100.31	4.598%	$104.9223	$104.92	$104.90	$104.90
Purchase #7	$57.71	4.592%	$60.36	$60.36	$60.35	$60.40
7 purchase totals =	$759.31		$799.0151	$799.01	$799.00	$799.00