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	$236.33	4.253%	$246.3811	$246.38	$246.40	$246.40
Purchase #2	$37.69	12.108%	$42.2535	$42.25	$42.25	$42.30
Purchase #3	$188.75	4.332%	$196.9267	$196.93	$196.95	$196.90
Purchase #4	$77.40	11.864%	$86.5827	$86.58	$86.60	$86.60
Purchase #5	$82.82	9.254%	$90.4842	$90.48	$90.50	$90.50
Purchase #6	$81.87	12.266%	$91.9122	$91.91	$91.90	$91.90
Purchase #7	$129.58	11.244%	$144.15	$144.15	$144.15	$144.20
7 purchase totals =	$834.44		$898.6904	$898.68	$898.75	$898.80