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	$90.45	12.439%	$101.7011	$101.70	$101.70	$101.70
Purchase #2	$194.86	3.103%	$200.9065	$200.91	$200.90	$200.90
Purchase #3	$46.61	12.245%	$52.3174	$52.32	$52.30	$52.30
Purchase #4	$185.54	3.285%	$191.635	$191.64	$191.65	$191.60
Purchase #5	$119.95	11.626%	$133.8954	$133.90	$133.90	$133.90
Purchase #6	$15.46	7.844%	$16.6727	$16.67	$16.65	$16.70
Purchase #7	$55.86	10.646%	$61.8069	$61.81	$61.80	$61.80
7 purchase totals =	$708.73		$758.9350	$758.95	$758.90	$758.90