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	$249.67	10.829%	$276.7068	$276.71	$276.70	$276.70
Purchase #2	$228.34	11.840%	$255.3755	$255.38	$255.40	$255.40
Purchase #3	$33.66	10.692%	$37.2589	$37.26	$37.25	$37.30
Purchase #4	$174.40	12.819%	$196.7563	$196.76	$196.75	$196.80
Purchase #5	$67.36	9.263%	$73.5996	$73.60	$73.60	$73.60
Purchase #6	$20.68	6.270%	$21.9766	$21.98	$22.00	$22.00
Purchase #7	$106.54	13.175%	$120.5766	$120.58	$120.60	$120.60
7 purchase totals =	$880.65		$982.2503	$982.27	$982.30	$982.40