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	$67.98	7.287%	$72.9337	$72.93	$72.95	$72.90
Purchase #2	$96.49	9.802%	$105.9479	$105.95	$105.95	$105.90
Purchase #3	$103.56	13.607%	$117.6514	$117.65	$117.65	$117.70
Purchase #4	$128.99	4.261%	$134.4863	$134.49	$134.50	$134.50
Purchase #5	$241.50	6.316%	$256.7531	$256.75	$256.75	$256.80
Purchase #6	$79.54	13.560%	$90.3256	$90.33	$90.35	$90.30
Purchase #7	$132.82	3.511%	$137.4833	$137.48	$137.50	$137.50
7 purchase totals =	$850.88		$915.5813	$915.58	$915.65	$915.60