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	$118.97	7.413%	$127.7892	$127.79	$127.80	$127.80
Purchase #2	$110.94	11.769%	$123.9965	$124.00	$124.00	$124.00
Purchase #3	$24.90	11.395%	$27.7374	$27.74	$27.75	$27.70
Purchase #4	$153.37	7.499%	$164.8712	$164.87	$164.85	$164.90
Purchase #5	$57.94	6.187%	$61.5247	$61.52	$61.50	$61.50
Purchase #6	$186.77	10.556%	$206.4854	$206.49	$206.50	$206.50
Purchase #7	$185.56	8.187%	$200.7518	$200.75	$200.75	$200.80
7 purchase totals =	$838.45		$913.1562	$913.16	$913.15	$913.20