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	$249.60	8.399%	$270.5639	$270.56	$270.55	$270.60
Purchase #2	$197.30	7.773%	$212.6361	$212.64	$212.65	$212.60
Purchase #3	$83.60	9.446%	$91.4969	$91.50	$91.50	$91.50
Purchase #4	$104.60	13.377%	$118.5923	$118.59	$118.60	$118.60
Purchase #5	$37.70	7.371%	$40.4789	$40.48	$40.50	$40.50
Purchase #6	$225.28	7.109%	$241.2952	$241.30	$241.30	$241.30
Purchase #7	$27.29	7.123%	$29.2339	$29.23	$29.25	$29.20
7 purchase totals =	$925.37		$1,004.2972	$1,004.30	$1,004.35	$1,004.30