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	$183.74	3.399%	$189.9853	$189.99	$190.00	$190.00
Purchase #2	$142.97	9.128%	$156.0203	$156.02	$156.00	$156.00
Purchase #3	$151.59	13.402%	$171.9061	$171.91	$171.90	$171.90
Purchase #4	$38.59	7.676%	$41.5522	$41.55	$41.55	$41.60
Purchase #5	$150.39	7.448%	$161.591	$161.59	$161.60	$161.60
Purchase #6	$40.26	6.685%	$42.9514	$42.95	$42.95	$43.00
Purchase #7	$29.73	10.329%	$32.8008	$32.80	$32.80	$32.80
7 purchase totals =	$737.27		$796.8071	$796.81	$796.80	$796.90