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	$109.86	12.411%	$123.4947	$123.49	$123.50	$123.50
Purchase #2	$145.53	11.440%	$162.1786	$162.18	$162.20	$162.20
Purchase #3	$226.37	10.597%	$250.3584	$250.36	$250.35	$250.40
Purchase #4	$6.35	13.296%	$7.1943	$7.19	$7.20	$7.20
Purchase #5	$21.94	9.766%	$24.0827	$24.08	$24.10	$24.10
Purchase #6	$136.86	5.637%	$144.5748	$144.57	$144.55	$144.60
Purchase #7	$210.51	10.869%	$233.3903	$233.39	$233.40	$233.40
7 purchase totals =	$857.42		$945.2738	$945.26	$945.30	$945.40