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	$128.35	12.801%	$144.7801	$144.78	$144.80	$144.80
Purchase #2	$32.36	3.185%	$33.3907	$33.39	$33.40	$33.40
Purchase #3	$217.33	10.821%	$240.8473	$240.85	$240.85	$240.80
Purchase #4	$181.87	4.204%	$189.5158	$189.52	$189.50	$189.50
Purchase #5	$169.72	7.217%	$181.9687	$181.97	$181.95	$182.00
Purchase #6	$18.69	10.459%	$20.6448	$20.64	$20.65	$20.60
Purchase #7	$206.27	3.356%	$213.1924	$213.19	$213.20	$213.20
7 purchase totals =	$954.59		$1,024.3398	$1,024.34	$1,024.35	$1,024.30