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	$227.87	13.294%	$258.163	$258.16	$258.15	$258.20
Purchase #2	$99.79	12.125%	$111.8895	$111.89	$111.90	$111.90
Purchase #3	$158.64	13.736%	$180.4308	$180.43	$180.45	$180.40
Purchase #4	$203.34	9.160%	$221.9659	$221.97	$221.95	$222.00
Purchase #5	$6.94	8.628%	$7.5388	$7.54	$7.55	$7.50
Purchase #6	$25.86	8.508%	$28.0602	$28.06	$28.05	$28.10
Purchase #7	$208.95	6.512%	$222.5568	$222.56	$222.55	$222.60
7 purchase totals =	$931.39		$1,030.6050	$1,030.61	$1,030.60	$1,030.70