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	$38.28	11.641%	$42.7362	$42.74	$42.75	$42.70
Purchase #2	$112.61	12.432%	$126.6097	$126.61	$126.60	$126.60
Purchase #3	$78.56	9.243%	$85.8213	$85.82	$85.80	$85.80
Purchase #4	$35.67	5.618%	$37.6739	$37.67	$37.65	$37.70
Purchase #5	$89.85	6.609%	$95.7882	$95.79	$95.80	$95.80
Purchase #6	$54.25	5.110%	$57.0222	$57.02	$57.00	$57.00
Purchase #7	$99.31	11.273%	$110.5052	$110.51	$110.50	$110.50
7 purchase totals =	$508.53		$556.1567	$556.16	$556.10	$556.10