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	$170.86	8.457%	$185.3096	$185.31	$185.30	$185.30
Purchase #2	$166.98	13.226%	$189.0648	$189.06	$189.05	$189.10
Purchase #3	$90.45	12.334%	$101.6061	$101.61	$101.60	$101.60
Purchase #4	$182.83	5.222%	$192.3774	$192.38	$192.40	$192.40
Purchase #5	$95.26	5.117%	$100.1345	$100.13	$100.15	$100.10
Purchase #6	$147.92	7.612%	$159.1797	$159.18	$159.20	$159.20
Purchase #7	$147.44	12.748%	$166.2357	$166.24	$166.25	$166.20
7 purchase totals =	$1,001.74		$1,093.9078	$1,093.91	$1,093.95	$1,093.90