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	$29.98	5.273%	$31.5608	$31.56	$31.55	$31.60
Purchase #2	$71.58	8.797%	$77.8769	$77.88	$77.90	$77.90
Purchase #3	$166.51	4.778%	$174.4658	$174.47	$174.45	$174.50
Purchase #4	$81.80	4.706%	$85.6495	$85.65	$85.65	$85.60
Purchase #5	$42.56	11.764%	$47.5668	$47.57	$47.55	$47.60
Purchase #6	$223.80	11.437%	$249.396	$249.40	$249.40	$249.40
Purchase #7	$113.33	9.344%	$123.9196	$123.92	$123.90	$123.90
7 purchase totals =	$729.56		$790.4354	$790.45	$790.40	$790.50