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	$13.31	4.338%	$13.8874	$13.89	$13.90	$13.90
Purchase #2	$176.67	4.333%	$184.3251	$184.33	$184.35	$184.30
Purchase #3	$249.42	13.514%	$283.1266	$283.13	$283.15	$283.10
Purchase #4	$121.43	7.782%	$130.8797	$130.88	$130.90	$130.90
Purchase #5	$76.92	5.219%	$80.9345	$80.93	$80.95	$80.90
Purchase #6	$86.78	5.675%	$91.7048	$91.70	$91.70	$91.70
Purchase #7	$100.45	8.808%	$109.2976	$109.30	$109.30	$109.30
7 purchase totals =	$824.98		$894.1557	$894.16	$894.25	$894.10