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	$39.56	5.871%	$41.8826	$41.88	$41.90	$41.90
Purchase #2	$174.93	6.640%	$186.5454	$186.55	$186.55	$186.50
Purchase #3	$142.95	6.641%	$152.4433	$152.44	$152.45	$152.40
Purchase #4	$157.35	10.118%	$173.2707	$173.27	$173.25	$173.30
Purchase #5	$204.61	8.448%	$221.8955	$221.90	$221.90	$221.90
Purchase #6	$153.68	7.667%	$165.4626	$165.46	$165.45	$165.50
Purchase #7	$184.76	7.317%	$198.2789	$198.28	$198.30	$198.30
7 purchase totals =	$1,057.84		$1,139.7790	$1,139.78	$1,139.80	$1,139.80