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	$160.56	4.522%	$167.8205	$167.82	$167.80	$167.80
Purchase #2	$234.49	12.743%	$264.3711	$264.37	$264.35	$264.40
Purchase #3	$131.43	12.236%	$147.5118	$147.51	$147.50	$147.50
Purchase #4	$241.82	6.283%	$257.0136	$257.01	$257.00	$257.00
Purchase #5	$182.47	7.473%	$196.106	$196.11	$196.10	$196.10
Purchase #6	$116.55	11.675%	$130.1572	$130.16	$130.15	$130.20
Purchase #7	$159.69	4.556%	$166.9655	$166.97	$166.95	$167.00
7 purchase totals =	$1,227.01		$1,329.9457	$1,329.95	$1,329.85	$1,330.00