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	$40.59	5.117%	$42.667	$42.67	$42.65	$42.70
Purchase #2	$85.66	7.112%	$91.7521	$91.75	$91.75	$91.80
Purchase #3	$85.47	4.510%	$89.3247	$89.32	$89.30	$89.30
Purchase #4	$60.57	4.558%	$63.3308	$63.33	$63.35	$63.30
Purchase #5	$148.75	9.752%	$163.2561	$163.26	$163.25	$163.30
Purchase #6	$108.81	3.353%	$112.4584	$112.46	$112.45	$112.50
Purchase #7	$85.40	3.602%	$88.4761	$88.48	$88.50	$88.50
7 purchase totals =	$615.25		$651.2652	$651.27	$651.25	$651.40