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	$35.78	5.442%	$37.7271	$37.73	$37.75	$37.70
Purchase #2	$29.58	12.342%	$33.2308	$33.23	$33.25	$33.20
Purchase #3	$245.60	4.480%	$256.6029	$256.60	$256.60	$256.60
Purchase #4	$138.39	5.317%	$145.7482	$145.75	$145.75	$145.70
Purchase #5	$213.80	11.673%	$238.7569	$238.76	$238.75	$238.80
Purchase #6	$128.86	9.213%	$140.7319	$140.73	$140.75	$140.70
Purchase #7	$34.53	12.152%	$38.7261	$38.73	$38.75	$38.70
7 purchase totals =	$826.54		$891.5239	$891.53	$891.60	$891.40