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	$188.25	11.726%	$210.3242	$210.32	$210.30	$210.30
Purchase #2	$109.64	7.745%	$118.1316	$118.13	$118.15	$118.10
Purchase #3	$173.45	5.347%	$182.7244	$182.72	$182.70	$182.70
Purchase #4	$58.31	13.739%	$66.3212	$66.32	$66.30	$66.30
Purchase #5	$100.76	11.528%	$112.3756	$112.38	$112.40	$112.40
Purchase #6	$155.49	6.664%	$165.8519	$165.85	$165.85	$165.90
Purchase #7	$64.61	4.819%	$67.7236	$67.72	$67.70	$67.70
7 purchase totals =	$850.51		$923.4525	$923.44	$923.40	$923.40