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	$6.83	4.723%	$7.1526	$7.15	$7.15	$7.20
Purchase #2	$127.32	13.498%	$144.5057	$144.51	$144.50	$144.50
Purchase #3	$14.63	8.413%	$15.8608	$15.86	$15.85	$15.90
Purchase #4	$123.83	6.198%	$131.505	$131.51	$131.50	$131.50
Purchase #5	$144.52	3.765%	$149.9612	$149.96	$149.95	$150.00
Purchase #6	$66.84	9.812%	$73.3983	$73.40	$73.40	$73.40
Purchase #7	$32.76	3.126%	$33.7841	$33.78	$33.80	$33.80
7 purchase totals =	$516.73		$556.1677	$556.17	$556.15	$556.30