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	$156.79	13.764%	$178.3706	$178.37	$178.35	$178.40
Purchase #2	$124.68	9.433%	$136.4411	$136.44	$136.45	$136.40
Purchase #3	$82.51	13.465%	$93.62	$93.62	$93.60	$93.60
Purchase #4	$66.70	9.110%	$72.7764	$72.78	$72.80	$72.80
Purchase #5	$94.67	3.808%	$98.275	$98.28	$98.30	$98.30
Purchase #6	$56.90	4.291%	$59.3416	$59.34	$59.35	$59.30
Purchase #7	$27.62	10.402%	$30.493	$30.49	$30.50	$30.50
7 purchase totals =	$609.87		$669.3177	$669.32	$669.35	$669.30