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	$75.96	3.365%	$78.5161	$78.52	$78.50	$78.50
Purchase #2	$150.33	5.408%	$158.4598	$158.46	$158.45	$158.50
Purchase #3	$47.91	9.434%	$52.4298	$52.43	$52.45	$52.40
Purchase #4	$100.47	3.596%	$104.0829	$104.08	$104.10	$104.10
Purchase #5	$129.80	8.285%	$140.5539	$140.55	$140.55	$140.60
Purchase #6	$213.79	3.496%	$221.2641	$221.26	$221.25	$221.30
Purchase #7	$220.56	6.686%	$235.3066	$235.31	$235.30	$235.30
7 purchase totals =	$938.82		$990.6132	$990.61	$990.60	$990.70