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	$30.60	8.114%	$33.0829	$33.08	$33.10	$33.10
Purchase #2	$16.80	11.423%	$18.7191	$18.72	$18.70	$18.70
Purchase #3	$214.36	13.164%	$242.5784	$242.58	$242.60	$242.60
Purchase #4	$103.83	5.809%	$109.8615	$109.86	$109.85	$109.90
Purchase #5	$7.55	13.653%	$8.5808	$8.58	$8.60	$8.60
Purchase #6	$55.29	7.851%	$59.6308	$59.63	$59.65	$59.60
Purchase #7	$123.30	11.475%	$137.4487	$137.45	$137.45	$137.40
7 purchase totals =	$551.73		$609.9022	$609.90	$609.95	$609.90