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	$221.54	12.642%	$249.5471	$249.55	$249.55	$249.50
Purchase #2	$130.27	13.741%	$148.1704	$148.17	$148.15	$148.20
Purchase #3	$48.93	11.311%	$54.4645	$54.46	$54.45	$54.50
Purchase #4	$125.69	6.144%	$133.4124	$133.41	$133.40	$133.40
Purchase #5	$52.89	3.725%	$54.8602	$54.86	$54.85	$54.90
Purchase #6	$102.96	9.686%	$112.9327	$112.93	$112.95	$112.90
Purchase #7	$235.28	11.410%	$262.1254	$262.13	$262.15	$262.10
7 purchase totals =	$917.56		$1,015.5127	$1,015.51	$1,015.50	$1,015.50