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	$150.77	5.764%	$159.4604	$159.46	$159.45	$159.50
Purchase #2	$92.86	5.289%	$97.7714	$97.77	$97.75	$97.80
Purchase #3	$18.57	9.790%	$20.388	$20.39	$20.40	$20.40
Purchase #4	$24.74	10.668%	$27.3793	$27.38	$27.40	$27.40
Purchase #5	$218.81	10.285%	$241.3146	$241.31	$241.30	$241.30
Purchase #6	$90.35	11.830%	$101.0384	$101.04	$101.05	$101.00
Purchase #7	$176.44	5.328%	$185.8407	$185.84	$185.85	$185.80
7 purchase totals =	$772.54		$833.1928	$833.19	$833.20	$833.20