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	$122.27	3.760%	$126.8674	$126.87	$126.85	$126.90
Purchase #2	$137.97	11.172%	$153.384	$153.38	$153.40	$153.40
Purchase #3	$169.34	13.333%	$191.9181	$191.92	$191.90	$191.90
Purchase #4	$121.55	7.296%	$130.4183	$130.42	$130.40	$130.40
Purchase #5	$78.44	13.760%	$89.2333	$89.23	$89.25	$89.20
Purchase #6	$92.57	12.788%	$104.4079	$104.41	$104.40	$104.40
Purchase #7	$41.33	11.487%	$46.0776	$46.08	$46.10	$46.10
7 purchase totals =	$763.47		$842.3066	$842.31	$842.30	$842.30