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	$51.27	13.208%	$58.0417	$58.04	$58.05	$58.00
Purchase #2	$82.73	8.316%	$89.6098	$89.61	$89.60	$89.60
Purchase #3	$185.48	10.834%	$205.5749	$205.57	$205.55	$205.60
Purchase #4	$28.76	7.694%	$30.9728	$30.97	$30.95	$31.00
Purchase #5	$246.81	12.818%	$278.4461	$278.45	$278.45	$278.40
Purchase #6	$203.43	3.373%	$210.2917	$210.29	$210.30	$210.30
Purchase #7	$176.64	13.533%	$200.5447	$200.54	$200.55	$200.50
7 purchase totals =	$975.12		$1,073.4817	$1,073.47	$1,073.45	$1,073.40