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	$68.62	3.188%	$70.8076	$70.81	$70.80	$70.80
Purchase #2	$135.78	5.319%	$143.0021	$143.00	$143.00	$143.00
Purchase #3	$51.89	10.782%	$57.4848	$57.48	$57.50	$57.50
Purchase #4	$80.48	6.231%	$85.4947	$85.49	$85.50	$85.50
Purchase #5	$25.47	11.687%	$28.4467	$28.45	$28.45	$28.40
Purchase #6	$236.42	3.142%	$243.8483	$243.85	$243.85	$243.80
Purchase #7	$209.39	10.693%	$231.7801	$231.78	$231.80	$231.80
7 purchase totals =	$808.05		$860.8643	$860.86	$860.90	$860.80