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	$60.74	10.363%	$67.0345	$67.03	$67.05	$67.00
Purchase #2	$126.51	7.368%	$135.8313	$135.83	$135.85	$135.80
Purchase #3	$151.68	9.527%	$166.1306	$166.13	$166.15	$166.10
Purchase #4	$178.77	12.153%	$200.4959	$200.50	$200.50	$200.50
Purchase #5	$250.38	7.390%	$268.8831	$268.88	$268.90	$268.90
Purchase #6	$120.29	11.515%	$134.1414	$134.14	$134.15	$134.10
Purchase #7	$134.79	3.292%	$139.2273	$139.23	$139.25	$139.20
7 purchase totals =	$1,023.16		$1,111.7441	$1,111.74	$1,111.85	$1,111.60