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	$98.93	11.802%	$110.6057	$110.61	$110.60	$110.60
Purchase #2	$103.69	10.529%	$114.6075	$114.61	$114.60	$114.60
Purchase #3	$221.52	13.674%	$251.8106	$251.81	$251.80	$251.80
Purchase #4	$77.52	7.469%	$83.31	$83.31	$83.30	$83.30
Purchase #5	$138.86	6.844%	$148.3636	$148.36	$148.35	$148.40
Purchase #6	$36.91	10.602%	$40.8232	$40.82	$40.80	$40.80
Purchase #7	$72.30	6.641%	$77.1014	$77.10	$77.10	$77.10
7 purchase totals =	$749.73		$826.6220	$826.62	$826.55	$826.60