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	$81.33	12.442%	$91.4491	$91.45	$91.45	$91.40
Purchase #2	$96.41	11.303%	$107.3072	$107.31	$107.30	$107.30
Purchase #3	$137.33	13.145%	$155.382	$155.38	$155.40	$155.40
Purchase #4	$176.50	11.209%	$196.2839	$196.28	$196.30	$196.30
Purchase #5	$109.26	4.801%	$114.5056	$114.51	$114.50	$114.50
Purchase #6	$71.79	11.203%	$79.8326	$79.83	$79.85	$79.80
Purchase #7	$39.73	6.845%	$42.4495	$42.45	$42.45	$42.40
7 purchase totals =	$712.35		$787.2099	$787.21	$787.25	$787.10