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	$19.93	11.148%	$22.1518	$22.15	$22.15	$22.20
Purchase #2	$216.50	9.158%	$236.3271	$236.33	$236.35	$236.30
Purchase #3	$31.58	12.274%	$35.4561	$35.46	$35.45	$35.50
Purchase #4	$100.73	4.318%	$105.0795	$105.08	$105.10	$105.10
Purchase #5	$87.57	13.589%	$99.4699	$99.47	$99.45	$99.50
Purchase #6	$231.50	13.827%	$263.5095	$263.51	$263.50	$263.50
Purchase #7	$209.38	7.850%	$225.8163	$225.82	$225.80	$225.80
7 purchase totals =	$897.19		$987.8102	$987.82	$987.80	$987.90