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	$66.63	3.223%	$68.7775	$68.78	$68.80	$68.80
Purchase #2	$110.67	5.301%	$116.5366	$116.54	$116.55	$116.50
Purchase #3	$105.96	3.442%	$109.6071	$109.61	$109.60	$109.60
Purchase #4	$47.38	5.823%	$50.1389	$50.14	$50.15	$50.10
Purchase #5	$170.86	12.270%	$191.8245	$191.82	$191.80	$191.80
Purchase #6	$178.27	3.456%	$184.431	$184.43	$184.45	$184.40
Purchase #7	$89.81	5.299%	$94.569	$94.57	$94.55	$94.60
7 purchase totals =	$769.58		$815.8846	$815.89	$815.90	$815.80