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	$160.35	11.498%	$178.787	$178.79	$178.80	$178.80
Purchase #2	$248.69	9.438%	$272.1614	$272.16	$272.15	$272.20
Purchase #3	$125.87	6.797%	$134.4254	$134.43	$134.45	$134.40
Purchase #4	$95.63	11.776%	$106.8914	$106.89	$106.90	$106.90
Purchase #5	$55.37	8.147%	$59.881	$59.88	$59.90	$59.90
Purchase #6	$131.55	11.148%	$146.2152	$146.22	$146.20	$146.20
Purchase #7	$72.88	6.830%	$77.8577	$77.86	$77.85	$77.90
7 purchase totals =	$890.34		$976.2191	$976.23	$976.25	$976.30