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	$37.44	7.353%	$40.193	$40.19	$40.20	$40.20
Purchase #2	$212.47	12.135%	$238.2532	$238.25	$238.25	$238.30
Purchase #3	$67.92	9.435%	$74.3283	$74.33	$74.35	$74.30
Purchase #4	$98.84	10.742%	$109.4574	$109.46	$109.45	$109.50
Purchase #5	$159.52	7.610%	$171.6595	$171.66	$171.65	$171.70
Purchase #6	$62.29	13.363%	$70.6138	$70.61	$70.60	$70.60
Purchase #7	$73.67	6.351%	$78.3488	$78.35	$78.35	$78.30
7 purchase totals =	$712.15		$782.8540	$782.85	$782.85	$782.90