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	$169.80	12.768%	$191.4801	$191.48	$191.50	$191.50
Purchase #2	$161.47	10.786%	$178.8862	$178.89	$178.90	$178.90
Purchase #3	$52.63	11.121%	$58.483	$58.48	$58.50	$58.50
Purchase #4	$45.89	12.372%	$51.5675	$51.57	$51.55	$51.60
Purchase #5	$39.40	7.839%	$42.4886	$42.49	$42.50	$42.50
Purchase #6	$13.87	8.333%	$15.0258	$15.03	$15.05	$15.00
Purchase #7	$85.65	6.542%	$91.2532	$91.25	$91.25	$91.30
7 purchase totals =	$568.71		$629.1844	$629.19	$629.25	$629.30