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	$78.47	4.220%	$81.7814	$81.78	$81.80	$81.80
Purchase #2	$250.58	5.310%	$263.8858	$263.89	$263.90	$263.90
Purchase #3	$186.78	5.261%	$196.6065	$196.61	$196.60	$196.60
Purchase #4	$142.79	9.423%	$156.2451	$156.25	$156.25	$156.20
Purchase #5	$204.76	9.175%	$223.5467	$223.55	$223.55	$223.50
Purchase #6	$91.65	12.591%	$103.1897	$103.19	$103.20	$103.20
Purchase #7	$173.36	12.795%	$195.5414	$195.54	$195.55	$195.50
7 purchase totals =	$1,128.39		$1,220.7966	$1,220.81	$1,220.85	$1,220.70