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	$140.62	13.287%	$159.3042	$159.30	$159.30	$159.30
Purchase #2	$196.76	13.147%	$222.628	$222.63	$222.65	$222.60
Purchase #3	$157.78	4.506%	$164.8896	$164.89	$164.90	$164.90
Purchase #4	$216.94	10.657%	$240.0593	$240.06	$240.05	$240.10
Purchase #5	$115.86	12.803%	$130.6936	$130.69	$130.70	$130.70
Purchase #6	$186.25	13.107%	$210.6618	$210.66	$210.65	$210.70
Purchase #7	$162.69	6.528%	$173.3104	$173.31	$173.30	$173.30
7 purchase totals =	$1,176.90		$1,301.5469	$1,301.54	$1,301.55	$1,301.60