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	$13.80	11.180%	$15.3428	$15.34	$15.35	$15.30
Purchase #2	$242.32	5.849%	$256.4933	$256.49	$256.50	$256.50
Purchase #3	$236.86	4.479%	$247.469	$247.47	$247.45	$247.50
Purchase #4	$130.98	4.215%	$136.5008	$136.50	$136.50	$136.50
Purchase #5	$19.41	12.871%	$21.9083	$21.91	$21.90	$21.90
Purchase #6	$96.95	3.727%	$100.5633	$100.56	$100.55	$100.60
Purchase #7	$227.97	6.685%	$243.2098	$243.21	$243.20	$243.20
7 purchase totals =	$968.29		$1,021.4873	$1,021.48	$1,021.45	$1,021.50