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	$45.70	9.185%	$49.8975	$49.90	$49.90	$49.90
Purchase #2	$74.38	9.355%	$81.3382	$81.34	$81.35	$81.30
Purchase #3	$93.51	10.806%	$103.6147	$103.61	$103.60	$103.60
Purchase #4	$144.52	12.387%	$162.4217	$162.42	$162.40	$162.40
Purchase #5	$244.68	8.118%	$264.5431	$264.54	$264.55	$264.50
Purchase #6	$245.47	7.235%	$263.2298	$263.23	$263.25	$263.20
Purchase #7	$170.61	10.269%	$188.1299	$188.13	$188.15	$188.10
7 purchase totals =	$1,018.87		$1,113.1749	$1,113.17	$1,113.20	$1,113.00