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	$207.72	6.384%	$220.9808	$220.98	$221.00	$221.00
Purchase #2	$170.60	5.466%	$179.925	$179.93	$179.95	$179.90
Purchase #3	$81.28	5.120%	$85.4415	$85.44	$85.45	$85.40
Purchase #4	$225.67	5.403%	$237.863	$237.86	$237.85	$237.90
Purchase #5	$140.64	8.300%	$152.3131	$152.31	$152.30	$152.30
Purchase #6	$35.40	6.189%	$37.5909	$37.59	$37.60	$37.60
Purchase #7	$9.89	12.666%	$11.1427	$11.14	$11.15	$11.10
7 purchase totals =	$871.20		$925.2570	$925.25	$925.30	$925.20