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	$40.65	4.596%	$42.5183	$42.52	$42.50	$42.50
Purchase #2	$127.97	4.305%	$133.4791	$133.48	$133.50	$133.50
Purchase #3	$36.35	4.162%	$37.8629	$37.86	$37.85	$37.90
Purchase #4	$160.83	13.457%	$182.4729	$182.47	$182.45	$182.50
Purchase #5	$246.36	13.268%	$279.047	$279.05	$279.05	$279.00
Purchase #6	$27.45	7.655%	$29.5513	$29.55	$29.55	$29.60
Purchase #7	$120.82	8.362%	$130.923	$130.92	$130.90	$130.90
7 purchase totals =	$760.43		$835.8545	$835.85	$835.80	$835.90