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	$111.83	9.148%	$122.0602	$122.06	$122.05	$122.10
Purchase #2	$25.91	10.488%	$28.6274	$28.63	$28.65	$28.60
Purchase #3	$18.99	11.172%	$21.1116	$21.11	$21.10	$21.10
Purchase #4	$220.52	9.687%	$241.8818	$241.88	$241.90	$241.90
Purchase #5	$177.36	6.338%	$188.6011	$188.60	$188.60	$188.60
Purchase #6	$84.33	6.464%	$89.7811	$89.78	$89.80	$89.80
Purchase #7	$86.74	4.425%	$90.5782	$90.58	$90.60	$90.60
7 purchase totals =	$725.68		$782.6414	$782.64	$782.70	$782.70