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	$29.91	13.283%	$33.8829	$33.88	$33.90	$33.90
Purchase #2	$204.95	8.531%	$222.4343	$222.43	$222.45	$222.40
Purchase #3	$22.90	12.745%	$25.8186	$25.82	$25.80	$25.80
Purchase #4	$47.59	12.631%	$53.6011	$53.60	$53.60	$53.60
Purchase #5	$209.72	9.113%	$228.8318	$228.83	$228.85	$228.80
Purchase #6	$125.40	13.480%	$142.3039	$142.30	$142.30	$142.30
Purchase #7	$43.31	6.535%	$46.1403	$46.14	$46.15	$46.10
7 purchase totals =	$683.78		$753.0129	$753.00	$753.05	$752.90