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	$234.46	6.243%	$249.0973	$249.10	$249.10	$249.10
Purchase #2	$24.69	7.699%	$26.5909	$26.59	$26.60	$26.60
Purchase #3	$244.33	10.308%	$269.5155	$269.52	$269.50	$269.50
Purchase #4	$61.82	9.817%	$67.8889	$67.89	$67.90	$67.90
Purchase #5	$43.45	9.758%	$47.6899	$47.69	$47.70	$47.70
Purchase #6	$178.32	8.492%	$193.4629	$193.46	$193.45	$193.50
Purchase #7	$17.32	7.367%	$18.596	$18.60	$18.60	$18.60
7 purchase totals =	$804.39		$872.8414	$872.85	$872.85	$872.90