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	$40.38	5.291%	$42.5165	$42.52	$42.50	$42.50
Purchase #2	$184.86	3.705%	$191.7091	$191.71	$191.70	$191.70
Purchase #3	$30.51	12.567%	$34.3442	$34.34	$34.35	$34.30
Purchase #4	$171.57	9.751%	$188.2998	$188.30	$188.30	$188.30
Purchase #5	$35.42	7.874%	$38.209	$38.21	$38.20	$38.20
Purchase #6	$159.56	4.263%	$166.362	$166.36	$166.35	$166.40
Purchase #7	$78.30	9.256%	$85.5474	$85.55	$85.55	$85.50
7 purchase totals =	$700.60		$746.9880	$746.99	$746.95	$746.90