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	$56.68	11.341%	$63.1081	$63.11	$63.10	$63.10
Purchase #2	$67.61	7.470%	$72.6605	$72.66	$72.65	$72.70
Purchase #3	$79.90	13.430%	$90.6306	$90.63	$90.65	$90.60
Purchase #4	$50.72	12.506%	$57.063	$57.06	$57.05	$57.10
Purchase #5	$50.30	3.143%	$51.8809	$51.88	$51.90	$51.90
Purchase #6	$27.83	3.583%	$28.8271	$28.83	$28.85	$28.80
Purchase #7	$8.87	9.681%	$9.7287	$9.73	$9.75	$9.70
7 purchase totals =	$341.91		$373.8989	$373.90	$373.95	$373.90