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	$20.63	9.859%	$22.6639	$22.66	$22.65	$22.70
Purchase #2	$36.85	5.173%	$38.7563	$38.76	$38.75	$38.80
Purchase #3	$39.47	8.261%	$42.7306	$42.73	$42.75	$42.70
Purchase #4	$237.62	3.355%	$245.5922	$245.59	$245.60	$245.60
Purchase #5	$72.89	10.873%	$80.8153	$80.82	$80.80	$80.80
Purchase #6	$89.44	12.548%	$100.6629	$100.66	$100.65	$100.70
Purchase #7	$233.32	7.487%	$250.7887	$250.79	$250.80	$250.80
7 purchase totals =	$730.22		$782.0099	$782.01	$782.00	$782.10