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	$125.77	4.143%	$130.9807	$130.98	$131.00	$131.00
Purchase #2	$227.64	12.711%	$256.5753	$256.58	$256.60	$256.60
Purchase #3	$65.40	5.599%	$69.0617	$69.06	$69.05	$69.10
Purchase #4	$68.55	5.272%	$72.164	$72.16	$72.15	$72.20
Purchase #5	$89.68	9.645%	$98.3296	$98.33	$98.35	$98.30
Purchase #6	$18.73	7.822%	$20.1951	$20.20	$20.20	$20.20
Purchase #7	$17.96	3.451%	$18.5798	$18.58	$18.60	$18.60
7 purchase totals =	$613.73		$665.8862	$665.89	$665.95	$666.00