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	$6.44	10.229%	$7.0987	$7.10	$7.10	$7.10
Purchase #2	$38.38	11.577%	$42.8233	$42.82	$42.80	$42.80
Purchase #3	$201.46	4.484%	$210.4935	$210.49	$210.50	$210.50
Purchase #4	$189.65	4.251%	$197.712	$197.71	$197.70	$197.70
Purchase #5	$142.87	8.173%	$154.5468	$154.55	$154.55	$154.50
Purchase #6	$76.78	6.811%	$82.0095	$82.01	$82.00	$82.00
Purchase #7	$75.37	8.256%	$81.5925	$81.59	$81.60	$81.60
7 purchase totals =	$730.95		$776.2763	$776.27	$776.25	$776.20