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	$110.83	12.404%	$124.5774	$124.58	$124.60	$124.60
Purchase #2	$39.48	8.692%	$42.9116	$42.91	$42.90	$42.90
Purchase #3	$174.73	9.504%	$191.3363	$191.34	$191.35	$191.30
Purchase #4	$127.96	11.479%	$142.6485	$142.65	$142.65	$142.60
Purchase #5	$65.67	7.169%	$70.3779	$70.38	$70.40	$70.40
Purchase #6	$177.40	6.801%	$189.465	$189.47	$189.45	$189.50
Purchase #7	$168.83	4.379%	$176.2231	$176.22	$176.20	$176.20
7 purchase totals =	$864.90		$937.5398	$937.55	$937.55	$937.50