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	$135.59	6.727%	$144.7111	$144.71	$144.70	$144.70
Purchase #2	$247.72	10.314%	$273.2698	$273.27	$273.25	$273.30
Purchase #3	$79.31	3.798%	$82.3222	$82.32	$82.30	$82.30
Purchase #4	$17.26	3.666%	$17.8928	$17.89	$17.90	$17.90
Purchase #5	$156.65	7.383%	$168.2155	$168.22	$168.20	$168.20
Purchase #6	$24.89	6.354%	$26.4715	$26.47	$26.45	$26.50
Purchase #7	$214.48	6.631%	$228.7022	$228.70	$228.70	$228.70
7 purchase totals =	$875.90		$941.5851	$941.58	$941.50	$941.60