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	$229.74	10.841%	$254.6461	$254.65	$254.65	$254.60
Purchase #2	$196.54	6.434%	$209.1854	$209.19	$209.20	$209.20
Purchase #3	$93.75	10.691%	$103.7728	$103.77	$103.75	$103.80
Purchase #4	$223.32	8.590%	$242.5032	$242.50	$242.50	$242.50
Purchase #5	$80.65	12.494%	$90.7264	$90.73	$90.75	$90.70
Purchase #6	$6.45	4.810%	$6.7602	$6.76	$6.75	$6.80
Purchase #7	$87.93	4.461%	$91.8526	$91.85	$91.85	$91.90
7 purchase totals =	$918.38		$999.4467	$999.45	$999.45	$999.50