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	$19.80	5.363%	$20.8619	$20.86	$20.85	$20.90
Purchase #2	$195.52	11.774%	$218.5405	$218.54	$218.55	$218.50
Purchase #3	$114.64	4.747%	$120.082	$120.08	$120.10	$120.10
Purchase #4	$60.89	11.230%	$67.7279	$67.73	$67.75	$67.70
Purchase #5	$32.48	3.850%	$33.7305	$33.73	$33.75	$33.70
Purchase #6	$169.75	4.576%	$177.5178	$177.52	$177.50	$177.50
Purchase #7	$136.60	3.646%	$141.5804	$141.58	$141.60	$141.60
7 purchase totals =	$729.68		$780.0410	$780.04	$780.10	$780.00