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	$170.51	3.522%	$176.5154	$176.52	$176.50	$176.50
Purchase #2	$217.56	5.694%	$229.9479	$229.95	$229.95	$229.90
Purchase #3	$80.29	3.228%	$82.8818	$82.88	$82.90	$82.90
Purchase #4	$162.75	6.873%	$173.9358	$173.94	$173.95	$173.90
Purchase #5	$7.61	13.364%	$8.627	$8.63	$8.65	$8.60
Purchase #6	$98.51	7.464%	$105.8628	$105.86	$105.85	$105.90
Purchase #7	$73.64	4.284%	$76.7947	$76.79	$76.80	$76.80
7 purchase totals =	$810.87		$854.5654	$854.57	$854.60	$854.50