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	$235.25	12.800%	$265.362	$265.36	$265.35	$265.40
Purchase #2	$91.33	8.252%	$98.8666	$98.87	$98.85	$98.90
Purchase #3	$88.73	4.737%	$92.9331	$92.93	$92.95	$92.90
Purchase #4	$249.61	13.269%	$282.7308	$282.73	$282.75	$282.70
Purchase #5	$195.97	13.417%	$222.2633	$222.26	$222.25	$222.30
Purchase #6	$27.47	8.346%	$29.7626	$29.76	$29.75	$29.80
Purchase #7	$98.90	12.521%	$111.2833	$111.28	$111.30	$111.30
7 purchase totals =	$987.26		$1,103.2017	$1,103.19	$1,103.20	$1,103.30