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	$239.79	12.210%	$269.0684	$269.07	$269.05	$269.10
Purchase #2	$95.62	10.634%	$105.7882	$105.79	$105.80	$105.80
Purchase #3	$181.42	3.170%	$187.171	$187.17	$187.15	$187.20
Purchase #4	$56.56	9.441%	$61.8998	$61.90	$61.90	$61.90
Purchase #5	$169.39	13.301%	$191.9206	$191.92	$191.90	$191.90
Purchase #6	$193.98	11.264%	$215.8299	$215.83	$215.85	$215.80
Purchase #7	$238.55	12.718%	$268.8888	$268.89	$268.90	$268.90
7 purchase totals =	$1,175.31		$1,300.5667	$1,300.57	$1,300.55	$1,300.60