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	$148.54	5.419%	$156.5894	$156.59	$156.60	$156.60
Purchase #2	$206.25	8.259%	$223.2842	$223.28	$223.30	$223.30
Purchase #3	$172.53	12.451%	$194.0117	$194.01	$194.00	$194.00
Purchase #4	$223.41	6.689%	$238.3539	$238.35	$238.35	$238.40
Purchase #5	$224.73	10.642%	$248.6458	$248.65	$248.65	$248.60
Purchase #6	$61.58	8.485%	$66.8051	$66.81	$66.80	$66.80
Purchase #7	$16.34	13.498%	$18.5456	$18.55	$18.55	$18.50
7 purchase totals =	$1,053.38		$1,146.2357	$1,146.24	$1,146.25	$1,146.20