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	$162.81	12.680%	$183.4543	$183.45	$183.45	$183.50
Purchase #2	$130.98	9.554%	$143.4938	$143.49	$143.50	$143.50
Purchase #3	$23.93	5.526%	$25.2524	$25.25	$25.25	$25.30
Purchase #4	$56.61	12.517%	$63.6959	$63.70	$63.70	$63.70
Purchase #5	$103.48	11.872%	$115.7651	$115.77	$115.75	$115.80
Purchase #6	$40.78	11.164%	$45.3327	$45.33	$45.35	$45.30
Purchase #7	$83.95	6.430%	$89.348	$89.35	$89.35	$89.30
7 purchase totals =	$602.54		$666.3422	$666.34	$666.35	$666.40