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	$108.49	13.652%	$123.3011	$123.30	$123.30	$123.30
Purchase #2	$94.36	5.650%	$99.6913	$99.69	$99.70	$99.70
Purchase #3	$196.65	8.629%	$213.6189	$213.62	$213.60	$213.60
Purchase #4	$141.33	4.126%	$147.1613	$147.16	$147.15	$147.20
Purchase #5	$20.60	7.384%	$22.1211	$22.12	$22.10	$22.10
Purchase #6	$182.65	12.621%	$205.7023	$205.70	$205.70	$205.70
Purchase #7	$37.52	12.769%	$42.3109	$42.31	$42.30	$42.30
7 purchase totals =	$781.60		$853.9069	$853.90	$853.85	$853.90