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	$140.25	11.475%	$156.3437	$156.34	$156.35	$156.30
Purchase #2	$231.47	11.648%	$258.4316	$258.43	$258.45	$258.40
Purchase #3	$82.57	7.712%	$88.9378	$88.94	$88.95	$88.90
Purchase #4	$142.32	6.633%	$151.7601	$151.76	$151.75	$151.80
Purchase #5	$50.99	7.800%	$54.9672	$54.97	$54.95	$55.00
Purchase #6	$30.57	10.760%	$33.8593	$33.86	$33.85	$33.90
Purchase #7	$158.55	7.130%	$169.8546	$169.85	$169.85	$169.90
7 purchase totals =	$836.72		$914.1543	$914.15	$914.15	$914.20