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	$209.89	10.392%	$231.7018	$231.70	$231.70	$231.70
Purchase #2	$139.32	11.421%	$155.2317	$155.23	$155.25	$155.20
Purchase #3	$19.35	7.275%	$20.7577	$20.76	$20.75	$20.80
Purchase #4	$181.77	12.177%	$203.9041	$203.90	$203.90	$203.90
Purchase #5	$189.40	3.345%	$195.7354	$195.74	$195.75	$195.70
Purchase #6	$196.54	13.554%	$223.179	$223.18	$223.20	$223.20
Purchase #7	$65.45	6.112%	$69.4503	$69.45	$69.45	$69.50
7 purchase totals =	$1,001.72		$1,099.9600	$1,099.96	$1,100.00	$1,100.00