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	$35.55	5.485%	$37.4999	$37.50	$37.50	$37.50
Purchase #2	$172.84	5.593%	$182.5069	$182.51	$182.50	$182.50
Purchase #3	$237.74	13.701%	$270.3128	$270.31	$270.30	$270.30
Purchase #4	$181.64	5.338%	$191.3359	$191.34	$191.35	$191.30
Purchase #5	$110.63	11.317%	$123.15	$123.15	$123.15	$123.20
Purchase #6	$18.61	13.448%	$21.1127	$21.11	$21.10	$21.10
Purchase #7	$157.97	13.602%	$179.4571	$179.46	$179.45	$179.50
7 purchase totals =	$914.98		$1,005.3753	$1,005.38	$1,005.35	$1,005.40