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	$135.58	5.815%	$143.464	$143.46	$143.45	$143.50
Purchase #2	$90.79	13.608%	$103.1447	$103.14	$103.15	$103.10
Purchase #3	$198.61	4.317%	$207.184	$207.18	$207.20	$207.20
Purchase #4	$113.47	9.262%	$123.9796	$123.98	$124.00	$124.00
Purchase #5	$39.90	12.593%	$44.9246	$44.92	$44.90	$44.90
Purchase #6	$249.91	3.389%	$258.3794	$258.38	$258.40	$258.40
Purchase #7	$174.94	6.127%	$185.6586	$185.66	$185.65	$185.70
7 purchase totals =	$1,003.20		$1,066.7349	$1,066.72	$1,066.75	$1,066.80