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	$235.77	6.199%	$250.3854	$250.39	$250.40	$250.40
Purchase #2	$89.87	10.445%	$99.2569	$99.26	$99.25	$99.30
Purchase #3	$114.59	7.715%	$123.4306	$123.43	$123.45	$123.40
Purchase #4	$225.37	6.687%	$240.4405	$240.44	$240.45	$240.40
Purchase #5	$85.59	11.192%	$95.1692	$95.17	$95.15	$95.20
Purchase #6	$235.32	13.524%	$267.1447	$267.14	$267.15	$267.10
Purchase #7	$118.67	12.626%	$133.6533	$133.65	$133.65	$133.70
7 purchase totals =	$1,105.18		$1,209.4806	$1,209.48	$1,209.50	$1,209.50