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	$172.55	4.693%	$180.6478	$180.65	$180.65	$180.60
Purchase #2	$44.90	5.809%	$47.5082	$47.51	$47.50	$47.50
Purchase #3	$162.57	3.594%	$168.4128	$168.41	$168.40	$168.40
Purchase #4	$52.57	3.408%	$54.3616	$54.36	$54.35	$54.40
Purchase #5	$225.59	3.817%	$234.2008	$234.20	$234.20	$234.20
Purchase #6	$247.60	4.220%	$258.0487	$258.05	$258.05	$258.00
Purchase #7	$53.53	3.355%	$55.3259	$55.33	$55.35	$55.30
7 purchase totals =	$959.31		$998.5058	$998.51	$998.50	$998.40