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	$18.45	7.840%	$19.8965	$19.90	$19.90	$19.90
Purchase #2	$92.46	7.497%	$99.3917	$99.39	$99.40	$99.40
Purchase #3	$187.51	4.809%	$196.5274	$196.53	$196.55	$196.50
Purchase #4	$194.99	13.209%	$220.7462	$220.75	$220.75	$220.70
Purchase #5	$212.46	4.432%	$221.8762	$221.88	$221.90	$221.90
Purchase #6	$38.83	12.651%	$43.7424	$43.74	$43.75	$43.70
Purchase #7	$159.66	13.528%	$181.2588	$181.26	$181.25	$181.30
7 purchase totals =	$904.36		$983.4392	$983.45	$983.50	$983.40