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	$33.88	3.689%	$35.1298	$35.13	$35.15	$35.10
Purchase #2	$99.35	12.612%	$111.88	$111.88	$111.90	$111.90
Purchase #3	$91.40	4.774%	$95.7634	$95.76	$95.75	$95.80
Purchase #4	$52.38	12.825%	$59.0977	$59.10	$59.10	$59.10
Purchase #5	$29.97	4.628%	$31.357	$31.36	$31.35	$31.40
Purchase #6	$64.31	4.593%	$67.2638	$67.26	$67.25	$67.30
Purchase #7	$172.46	9.851%	$189.449	$189.45	$189.45	$189.40
7 purchase totals =	$543.75		$589.9407	$589.94	$589.95	$590.00