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	$130.61	5.180%	$137.3756	$137.38	$137.40	$137.40
Purchase #2	$104.95	3.212%	$108.321	$108.32	$108.30	$108.30
Purchase #3	$67.33	4.454%	$70.3289	$70.33	$70.35	$70.30
Purchase #4	$183.25	6.275%	$194.7489	$194.75	$194.75	$194.70
Purchase #5	$101.27	7.510%	$108.8754	$108.88	$108.90	$108.90
Purchase #6	$48.39	8.185%	$52.3507	$52.35	$52.35	$52.40
Purchase #7	$247.51	4.825%	$259.4524	$259.45	$259.45	$259.50
7 purchase totals =	$883.31		$931.4529	$931.46	$931.50	$931.50