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	$173.67	5.558%	$183.3226	$183.32	$183.30	$183.30
Purchase #2	$69.53	6.801%	$74.2587	$74.26	$74.25	$74.30
Purchase #3	$99.35	4.263%	$103.5853	$103.59	$103.60	$103.60
Purchase #4	$89.31	3.782%	$92.6877	$92.69	$92.70	$92.70
Purchase #5	$167.69	12.275%	$188.2739	$188.27	$188.25	$188.30
Purchase #6	$168.68	11.353%	$187.8302	$187.83	$187.85	$187.80
Purchase #7	$183.87	13.848%	$209.3323	$209.33	$209.35	$209.30
7 purchase totals =	$952.10		$1,039.2907	$1,039.29	$1,039.30	$1,039.30