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	$100.38	11.462%	$111.8856	$111.89	$111.90	$111.90
Purchase #2	$179.55	5.515%	$189.4522	$189.45	$189.45	$189.50
Purchase #3	$167.56	12.378%	$188.3006	$188.30	$188.30	$188.30
Purchase #4	$120.66	8.214%	$130.571	$130.57	$130.55	$130.60
Purchase #5	$92.30	9.208%	$100.799	$100.80	$100.80	$100.80
Purchase #6	$182.76	13.219%	$206.919	$206.92	$206.90	$206.90
Purchase #7	$143.46	6.157%	$152.2928	$152.29	$152.30	$152.30
7 purchase totals =	$986.67		$1,080.2202	$1,080.22	$1,080.20	$1,080.30