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	$29.38	13.452%	$33.3322	$33.33	$33.35	$33.30
Purchase #2	$105.86	6.257%	$112.4837	$112.48	$112.50	$112.50
Purchase #3	$142.63	9.158%	$155.6921	$155.69	$155.70	$155.70
Purchase #4	$135.25	6.764%	$144.3983	$144.40	$144.40	$144.40
Purchase #5	$160.40	6.444%	$170.7362	$170.74	$170.75	$170.70
Purchase #6	$48.45	13.137%	$54.8149	$54.81	$54.80	$54.80
Purchase #7	$85.81	6.558%	$91.4374	$91.44	$91.45	$91.40
7 purchase totals =	$707.78		$762.8948	$762.89	$762.95	$762.80