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	$124.51	9.531%	$136.377	$136.38	$136.40	$136.40
Purchase #2	$89.35	7.611%	$96.1504	$96.15	$96.15	$96.20
Purchase #3	$108.82	3.755%	$112.9062	$112.91	$112.90	$112.90
Purchase #4	$42.83	5.787%	$45.3086	$45.31	$45.30	$45.30
Purchase #5	$175.46	12.774%	$197.8733	$197.87	$197.85	$197.90
Purchase #6	$29.52	7.656%	$31.7801	$31.78	$31.80	$31.80
Purchase #7	$135.72	4.558%	$141.9061	$141.91	$141.90	$141.90
7 purchase totals =	$706.21		$762.3017	$762.31	$762.30	$762.40