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	$7.46	4.652%	$7.807	$7.81	$7.80	$7.80
Purchase #2	$113.58	9.326%	$124.1725	$124.17	$124.15	$124.20
Purchase #3	$10.49	3.598%	$10.8674	$10.87	$10.85	$10.90
Purchase #4	$47.85	13.569%	$54.3428	$54.34	$54.35	$54.30
Purchase #5	$166.27	3.305%	$171.7652	$171.77	$171.75	$171.80
Purchase #6	$97.56	12.230%	$109.4916	$109.49	$109.50	$109.50
Purchase #7	$153.70	9.793%	$168.7518	$168.75	$168.75	$168.80
7 purchase totals =	$596.91		$647.1983	$647.20	$647.15	$647.30