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	$51.90	6.615%	$55.3332	$55.33	$55.35	$55.30
Purchase #2	$154.31	3.346%	$159.4732	$159.47	$159.45	$159.50
Purchase #3	$244.89	10.409%	$270.3806	$270.38	$270.40	$270.40
Purchase #4	$154.26	9.357%	$168.6941	$168.69	$168.70	$168.70
Purchase #5	$138.30	10.611%	$152.975	$152.98	$153.00	$153.00
Purchase #6	$219.53	12.136%	$246.1722	$246.17	$246.15	$246.20
Purchase #7	$217.89	12.629%	$245.4073	$245.41	$245.40	$245.40
7 purchase totals =	$1,181.08		$1,298.4356	$1,298.43	$1,298.45	$1,298.50