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	$69.73	12.513%	$78.4553	$78.46	$78.45	$78.50
Purchase #2	$184.88	10.243%	$203.8173	$203.82	$203.80	$203.80
Purchase #3	$128.30	9.107%	$139.9843	$139.98	$140.00	$140.00
Purchase #4	$63.52	13.861%	$72.3245	$72.32	$72.30	$72.30
Purchase #5	$172.69	7.322%	$185.3344	$185.33	$185.35	$185.30
Purchase #6	$98.80	6.586%	$105.307	$105.31	$105.30	$105.30
Purchase #7	$12.28	7.301%	$13.1766	$13.18	$13.20	$13.20
7 purchase totals =	$730.20		$798.3994	$798.40	$798.40	$798.40