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	$91.80	5.210%	$96.5828	$96.58	$96.60	$96.60
Purchase #2	$41.50	9.470%	$45.4301	$45.43	$45.45	$45.40
Purchase #3	$52.39	12.185%	$58.7737	$58.77	$58.75	$58.80
Purchase #4	$229.71	3.752%	$238.3287	$238.33	$238.35	$238.30
Purchase #5	$159.78	3.860%	$165.9475	$165.95	$165.95	$165.90
Purchase #6	$40.86	5.231%	$42.9974	$43.00	$43.00	$43.00
Purchase #7	$177.69	12.738%	$200.3242	$200.32	$200.30	$200.30
7 purchase totals =	$793.73		$848.3844	$848.38	$848.40	$848.30