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	$113.71	13.777%	$129.3758	$129.38	$129.40	$129.40
Purchase #2	$123.98	12.491%	$139.4663	$139.47	$139.45	$139.50
Purchase #3	$224.50	11.598%	$250.5375	$250.54	$250.55	$250.50
Purchase #4	$229.34	6.108%	$243.3481	$243.35	$243.35	$243.30
Purchase #5	$74.50	9.687%	$81.7168	$81.72	$81.70	$81.70
Purchase #6	$247.35	4.515%	$258.5179	$258.52	$258.50	$258.50
Purchase #7	$172.39	6.110%	$182.923	$182.92	$182.90	$182.90
7 purchase totals =	$1,185.77		$1,285.8854	$1,285.90	$1,285.85	$1,285.80