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	$227.76	12.334%	$255.8519	$255.85	$255.85	$255.90
Purchase #2	$73.86	7.180%	$79.1631	$79.16	$79.15	$79.20
Purchase #3	$189.99	13.611%	$215.8495	$215.85	$215.85	$215.80
Purchase #4	$141.93	6.611%	$151.313	$151.31	$151.30	$151.30
Purchase #5	$237.28	11.655%	$264.935	$264.94	$264.95	$264.90
Purchase #6	$117.72	4.653%	$123.1975	$123.20	$123.20	$123.20
Purchase #7	$143.94	4.341%	$150.1884	$150.19	$150.20	$150.20
7 purchase totals =	$1,132.48		$1,240.4984	$1,240.50	$1,240.50	$1,240.50