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	$126.36	10.295%	$139.3688	$139.37	$139.35	$139.40
Purchase #2	$210.47	6.375%	$223.8875	$223.89	$223.90	$223.90
Purchase #3	$235.32	3.263%	$242.9985	$243.00	$243.00	$243.00
Purchase #4	$62.94	13.422%	$71.3878	$71.39	$71.40	$71.40
Purchase #5	$193.45	6.851%	$206.7033	$206.70	$206.70	$206.70
Purchase #6	$247.47	4.515%	$258.6433	$258.64	$258.65	$258.60
Purchase #7	$174.86	12.138%	$196.0845	$196.08	$196.10	$196.10
7 purchase totals =	$1,250.87		$1,339.0737	$1,339.07	$1,339.10	$1,339.10