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	$48.59	4.737%	$50.8917	$50.89	$50.90	$50.90
Purchase #2	$208.75	7.849%	$225.1348	$225.13	$225.15	$225.10
Purchase #3	$153.68	9.368%	$168.0767	$168.08	$168.10	$168.10
Purchase #4	$33.47	11.465%	$37.3073	$37.31	$37.30	$37.30
Purchase #5	$57.31	7.578%	$61.653	$61.65	$61.65	$61.70
Purchase #6	$248.84	5.742%	$263.1284	$263.13	$263.15	$263.10
Purchase #7	$38.54	12.496%	$43.356	$43.36	$43.35	$43.40
7 purchase totals =	$789.18		$849.5479	$849.55	$849.60	$849.60