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	$18.86	7.721%	$20.3162	$20.32	$20.30	$20.30
Purchase #2	$82.95	8.514%	$90.0124	$90.01	$90.00	$90.00
Purchase #3	$69.89	5.159%	$73.4956	$73.50	$73.50	$73.50
Purchase #4	$245.98	10.468%	$271.7292	$271.73	$271.75	$271.70
Purchase #5	$34.60	9.686%	$37.9514	$37.95	$37.95	$38.00
Purchase #6	$30.56	3.347%	$31.5828	$31.58	$31.60	$31.60
Purchase #7	$102.86	5.865%	$108.8927	$108.89	$108.90	$108.90
7 purchase totals =	$585.70		$633.9803	$633.98	$634.00	$634.00