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	$90.34	12.167%	$101.3317	$101.33	$101.35	$101.30
Purchase #2	$103.64	12.760%	$116.8645	$116.86	$116.85	$116.90
Purchase #3	$148.42	11.208%	$165.0549	$165.05	$165.05	$165.10
Purchase #4	$148.70	12.398%	$167.1358	$167.14	$167.15	$167.10
Purchase #5	$100.39	4.834%	$105.2429	$105.24	$105.25	$105.20
Purchase #6	$5.97	8.739%	$6.4917	$6.49	$6.50	$6.50
Purchase #7	$215.86	5.745%	$228.2612	$228.26	$228.25	$228.30
7 purchase totals =	$813.32		$890.3827	$890.37	$890.40	$890.40