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	$112.51	6.490%	$119.8119	$119.81	$119.80	$119.80
Purchase #2	$37.55	12.735%	$42.332	$42.33	$42.35	$42.30
Purchase #3	$88.25	13.266%	$99.9572	$99.96	$99.95	$100.00
Purchase #4	$174.81	5.537%	$184.4892	$184.49	$184.50	$184.50
Purchase #5	$166.69	5.573%	$175.9796	$175.98	$176.00	$176.00
Purchase #6	$98.78	13.332%	$111.9493	$111.95	$111.95	$111.90
Purchase #7	$139.44	10.728%	$154.3991	$154.40	$154.40	$154.40
7 purchase totals =	$818.03		$888.9183	$888.92	$888.95	$888.90