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	$120.35	9.792%	$132.1347	$132.13	$132.15	$132.10
Purchase #2	$250.48	7.258%	$268.6598	$268.66	$268.65	$268.70
Purchase #3	$224.41	8.489%	$243.4602	$243.46	$243.45	$243.50
Purchase #4	$12.40	8.232%	$13.4208	$13.42	$13.40	$13.40
Purchase #5	$111.53	7.604%	$120.0107	$120.01	$120.00	$120.00
Purchase #6	$70.90	13.446%	$80.4332	$80.43	$80.45	$80.40
Purchase #7	$209.69	6.163%	$222.6132	$222.61	$222.60	$222.60
7 purchase totals =	$999.76		$1,080.7326	$1,080.72	$1,080.70	$1,080.70