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	$227.47	6.704%	$242.7196	$242.72	$242.70	$242.70
Purchase #2	$125.91	11.852%	$140.8329	$140.83	$140.85	$140.80
Purchase #3	$36.54	11.598%	$40.7779	$40.78	$40.80	$40.80
Purchase #4	$171.30	5.235%	$180.2676	$180.27	$180.25	$180.30
Purchase #5	$162.29	12.297%	$182.2468	$182.25	$182.25	$182.20
Purchase #6	$57.59	10.104%	$63.4089	$63.41	$63.40	$63.40
Purchase #7	$43.46	5.675%	$45.9264	$45.93	$45.95	$45.90
7 purchase totals =	$824.56		$896.1801	$896.19	$896.20	$896.10