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	$236.88	3.567%	$245.3295	$245.33	$245.35	$245.30
Purchase #2	$142.86	13.207%	$161.7275	$161.73	$161.75	$161.70
Purchase #3	$132.53	3.826%	$137.6006	$137.60	$137.60	$137.60
Purchase #4	$37.44	13.249%	$42.4004	$42.40	$42.40	$42.40
Purchase #5	$66.56	3.796%	$69.0866	$69.09	$69.10	$69.10
Purchase #6	$220.97	13.305%	$250.3701	$250.37	$250.35	$250.40
Purchase #7	$57.73	3.741%	$59.8897	$59.89	$59.90	$59.90
7 purchase totals =	$894.97		$966.4044	$966.41	$966.45	$966.40