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	$128.41	9.671%	$140.8285	$140.83	$140.85	$140.80
Purchase #2	$62.83	8.439%	$68.1322	$68.13	$68.15	$68.10
Purchase #3	$37.29	10.562%	$41.2286	$41.23	$41.25	$41.20
Purchase #4	$102.35	6.757%	$109.2658	$109.27	$109.25	$109.30
Purchase #5	$142.26	4.751%	$149.0188	$149.02	$149.00	$149.00
Purchase #6	$172.91	8.304%	$187.2684	$187.27	$187.25	$187.30
Purchase #7	$82.34	8.284%	$89.161	$89.16	$89.15	$89.20
7 purchase totals =	$728.39		$784.9033	$784.91	$784.90	$784.90