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	$155.88	12.505%	$175.3728	$175.37	$175.35	$175.40
Purchase #2	$55.89	5.775%	$59.1176	$59.12	$59.10	$59.10
Purchase #3	$132.41	12.172%	$148.5269	$148.53	$148.55	$148.50
Purchase #4	$93.70	12.557%	$105.4659	$105.47	$105.45	$105.50
Purchase #5	$81.40	8.121%	$88.0105	$88.01	$88.00	$88.00
Purchase #6	$46.79	4.542%	$48.9152	$48.92	$48.90	$48.90
Purchase #7	$162.65	11.217%	$180.8945	$180.89	$180.90	$180.90
7 purchase totals =	$728.72		$806.3034	$806.31	$806.25	$806.30