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	$155.79	10.311%	$171.8535	$171.85	$171.85	$171.90
Purchase #2	$227.48	4.305%	$237.273	$237.27	$237.25	$237.30
Purchase #3	$113.30	13.687%	$128.8074	$128.81	$128.80	$128.80
Purchase #4	$225.81	3.434%	$233.5643	$233.56	$233.55	$233.60
Purchase #5	$82.71	9.823%	$90.8346	$90.83	$90.85	$90.80
Purchase #6	$71.33	3.336%	$73.7096	$73.71	$73.70	$73.70
Purchase #7	$130.75	11.425%	$145.6882	$145.69	$145.70	$145.70
7 purchase totals =	$1,007.17		$1,081.7306	$1,081.72	$1,081.70	$1,081.80