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	$46.45	12.131%	$52.0848	$52.08	$52.10	$52.10
Purchase #2	$212.45	7.547%	$228.4836	$228.48	$228.50	$228.50
Purchase #3	$205.95	3.653%	$213.4734	$213.47	$213.45	$213.50
Purchase #4	$179.64	13.456%	$203.8124	$203.81	$203.80	$203.80
Purchase #5	$116.93	12.807%	$131.9052	$131.91	$131.90	$131.90
Purchase #6	$211.70	5.768%	$223.9109	$223.91	$223.90	$223.90
Purchase #7	$48.60	7.156%	$52.0778	$52.08	$52.10	$52.10
7 purchase totals =	$1,021.72		$1,105.7481	$1,105.74	$1,105.75	$1,105.80