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	$81.73	11.110%	$90.8102	$90.81	$90.80	$90.80
Purchase #2	$175.98	12.845%	$198.5846	$198.58	$198.60	$198.60
Purchase #3	$211.71	12.671%	$238.5358	$238.54	$238.55	$238.50
Purchase #4	$112.55	6.789%	$120.191	$120.19	$120.20	$120.20
Purchase #5	$225.61	10.841%	$250.0684	$250.07	$250.05	$250.10
Purchase #6	$75.96	12.272%	$85.2818	$85.28	$85.30	$85.30
Purchase #7	$37.84	7.559%	$40.7003	$40.70	$40.70	$40.70
7 purchase totals =	$921.38		$1,024.1721	$1,024.17	$1,024.20	$1,024.20