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	$134.27	3.190%	$138.5532	$138.55	$138.55	$138.60
Purchase #2	$231.76	7.395%	$248.8987	$248.90	$248.90	$248.90
Purchase #3	$42.71	11.251%	$47.5153	$47.52	$47.50	$47.50
Purchase #4	$106.54	4.744%	$111.5943	$111.59	$111.60	$111.60
Purchase #5	$163.61	6.835%	$174.7927	$174.79	$174.80	$174.80
Purchase #6	$40.54	4.308%	$42.2865	$42.29	$42.30	$42.30
Purchase #7	$92.48	4.269%	$96.428	$96.43	$96.45	$96.40
7 purchase totals =	$811.91		$860.0687	$860.07	$860.10	$860.10