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	$72.79	6.413%	$77.458	$77.46	$77.45	$77.50
Purchase #2	$77.70	12.604%	$87.4933	$87.49	$87.50	$87.50
Purchase #3	$64.90	10.834%	$71.9313	$71.93	$71.95	$71.90
Purchase #4	$148.73	9.618%	$163.0349	$163.03	$163.05	$163.00
Purchase #5	$79.56	12.455%	$89.4692	$89.47	$89.45	$89.50
Purchase #6	$233.35	10.726%	$258.3791	$258.38	$258.40	$258.40
Purchase #7	$49.87	13.235%	$56.4703	$56.47	$56.45	$56.50
7 purchase totals =	$726.90		$804.2361	$804.23	$804.25	$804.30