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	$194.52	8.752%	$211.5444	$211.54	$211.55	$211.50
Purchase #2	$247.56	12.790%	$279.2229	$279.22	$279.20	$279.20
Purchase #3	$139.76	7.499%	$150.2406	$150.24	$150.25	$150.20
Purchase #4	$45.92	10.552%	$50.7655	$50.77	$50.75	$50.80
Purchase #5	$52.71	12.564%	$59.3325	$59.33	$59.35	$59.30
Purchase #6	$30.54	6.284%	$32.4591	$32.46	$32.45	$32.50
Purchase #7	$73.39	10.719%	$81.2567	$81.26	$81.25	$81.30
7 purchase totals =	$784.40		$864.8217	$864.82	$864.80	$864.80