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	$27.36	11.269%	$30.4432	$30.44	$30.45	$30.40
Purchase #2	$191.42	12.326%	$215.0144	$215.01	$215.00	$215.00
Purchase #3	$100.92	9.503%	$110.5104	$110.51	$110.50	$110.50
Purchase #4	$149.80	11.597%	$167.1723	$167.17	$167.15	$167.20
Purchase #5	$210.65	5.698%	$222.6528	$222.65	$222.65	$222.70
Purchase #6	$139.62	9.292%	$152.5935	$152.59	$152.60	$152.60
Purchase #7	$190.69	7.741%	$205.4513	$205.45	$205.45	$205.50
7 purchase totals =	$1,010.46		$1,103.8379	$1,103.82	$1,103.80	$1,103.90