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	$121.44	13.578%	$137.9291	$137.93	$137.95	$137.90
Purchase #2	$89.96	13.568%	$102.1658	$102.17	$102.15	$102.20
Purchase #3	$141.67	8.486%	$153.6921	$153.69	$153.70	$153.70
Purchase #4	$143.96	8.846%	$156.6947	$156.69	$156.70	$156.70
Purchase #5	$67.85	4.636%	$70.9955	$71.00	$71.00	$71.00
Purchase #6	$79.81	13.668%	$90.7184	$90.72	$90.70	$90.70
Purchase #7	$95.77	8.835%	$104.2313	$104.23	$104.25	$104.20
7 purchase totals =	$740.46		$816.4269	$816.43	$816.45	$816.40