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	$159.60	13.181%	$180.6369	$180.64	$180.65	$180.60
Purchase #2	$93.49	7.304%	$100.3185	$100.32	$100.30	$100.30
Purchase #3	$171.38	9.403%	$187.4949	$187.49	$187.50	$187.50
Purchase #4	$83.71	9.582%	$91.7311	$91.73	$91.75	$91.70
Purchase #5	$209.40	13.478%	$237.6229	$237.62	$237.60	$237.60
Purchase #6	$222.28	12.481%	$250.0228	$250.02	$250.00	$250.00
Purchase #7	$99.42	10.584%	$109.9426	$109.94	$109.95	$109.90
7 purchase totals =	$1,039.28		$1,157.7697	$1,157.76	$1,157.75	$1,157.60