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	$224.82	13.669%	$255.5506	$255.55	$255.55	$255.60
Purchase #2	$159.26	6.608%	$169.7839	$169.78	$169.80	$169.80
Purchase #3	$220.31	4.321%	$229.8296	$229.83	$229.85	$229.80
Purchase #4	$6.92	8.306%	$7.4948	$7.49	$7.50	$7.50
Purchase #5	$18.37	11.842%	$20.5454	$20.55	$20.55	$20.50
Purchase #6	$203.82	5.597%	$215.2278	$215.23	$215.25	$215.20
Purchase #7	$71.56	7.294%	$76.7796	$76.78	$76.80	$76.80
7 purchase totals =	$905.06		$975.2117	$975.21	$975.30	$975.20