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	$72.91	9.518%	$79.8496	$79.85	$79.85	$79.80
Purchase #2	$82.44	8.450%	$89.4062	$89.41	$89.40	$89.40
Purchase #3	$167.26	13.462%	$189.7765	$189.78	$189.80	$189.80
Purchase #4	$202.94	4.190%	$211.4432	$211.44	$211.45	$211.40
Purchase #5	$121.39	13.654%	$137.9646	$137.96	$137.95	$138.00
Purchase #6	$123.60	6.420%	$131.5351	$131.54	$131.55	$131.50
Purchase #7	$176.87	13.467%	$200.6891	$200.69	$200.70	$200.70
7 purchase totals =	$947.41		$1,040.6643	$1,040.67	$1,040.70	$1,040.60