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	$31.41	5.701%	$33.2007	$33.20	$33.20	$33.20
Purchase #2	$127.81	10.575%	$141.3259	$141.33	$141.35	$141.30
Purchase #3	$177.96	10.282%	$196.2578	$196.26	$196.25	$196.30
Purchase #4	$224.96	13.157%	$254.558	$254.56	$254.55	$254.60
Purchase #5	$105.44	12.845%	$118.9838	$118.98	$119.00	$119.00
Purchase #6	$237.75	7.462%	$255.4909	$255.49	$255.50	$255.50
Purchase #7	$177.81	7.827%	$191.7272	$191.73	$191.75	$191.70
7 purchase totals =	$1,083.14		$1,191.5443	$1,191.55	$1,191.60	$1,191.60