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	$100.69	3.224%	$103.9362	$103.94	$103.95	$103.90
Purchase #2	$83.56	7.562%	$89.8788	$89.88	$89.90	$89.90
Purchase #3	$20.26	13.110%	$22.9161	$22.92	$22.90	$22.90
Purchase #4	$66.70	8.333%	$72.2581	$72.26	$72.25	$72.30
Purchase #5	$116.30	8.698%	$126.4158	$126.42	$126.40	$126.40
Purchase #6	$159.96	7.681%	$172.2465	$172.25	$172.25	$172.20
Purchase #7	$28.98	8.175%	$31.3491	$31.35	$31.35	$31.30
7 purchase totals =	$576.45		$619.0006	$619.02	$619.00	$618.90