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	$249.52	12.727%	$281.2764	$281.28	$281.30	$281.30
Purchase #2	$39.76	7.818%	$42.8684	$42.87	$42.85	$42.90
Purchase #3	$60.97	7.333%	$65.4409	$65.44	$65.45	$65.40
Purchase #4	$124.81	13.711%	$141.9227	$141.92	$141.90	$141.90
Purchase #5	$188.78	10.155%	$207.9506	$207.95	$207.95	$208.00
Purchase #6	$171.78	9.138%	$187.4773	$187.48	$187.50	$187.50
Purchase #7	$209.47	3.346%	$216.4789	$216.48	$216.50	$216.50
7 purchase totals =	$1,045.09		$1,143.4152	$1,143.42	$1,143.45	$1,143.50