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	$49.71	6.191%	$52.7875	$52.79	$52.80	$52.80
Purchase #2	$101.57	11.257%	$113.0037	$113.00	$113.00	$113.00
Purchase #3	$45.61	11.172%	$50.7055	$50.71	$50.70	$50.70
Purchase #4	$90.55	12.250%	$101.6424	$101.64	$101.65	$101.60
Purchase #5	$54.61	13.146%	$61.789	$61.79	$61.80	$61.80
Purchase #6	$110.35	11.555%	$123.1009	$123.10	$123.10	$123.10
Purchase #7	$234.55	13.419%	$266.0243	$266.02	$266.00	$266.00
7 purchase totals =	$686.95		$769.0533	$769.05	$769.05	$769.00