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	$39.32	7.221%	$42.1593	$42.16	$42.15	$42.20
Purchase #2	$117.37	12.196%	$131.6844	$131.68	$131.70	$131.70
Purchase #3	$124.97	11.735%	$139.6352	$139.64	$139.65	$139.60
Purchase #4	$228.32	8.867%	$248.5651	$248.57	$248.55	$248.60
Purchase #5	$184.40	5.143%	$193.8837	$193.88	$193.90	$193.90
Purchase #6	$125.52	3.412%	$129.8027	$129.80	$129.80	$129.80
Purchase #7	$52.35	13.324%	$59.3251	$59.33	$59.35	$59.30
7 purchase totals =	$872.25		$945.0555	$945.06	$945.10	$945.10