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	$41.79	3.843%	$43.396	$43.40	$43.40	$43.40
Purchase #2	$103.58	9.220%	$113.1301	$113.13	$113.15	$113.10
Purchase #3	$31.89	13.597%	$36.2261	$36.23	$36.25	$36.20
Purchase #4	$64.53	9.286%	$70.5223	$70.52	$70.50	$70.50
Purchase #5	$60.79	11.418%	$67.731	$67.73	$67.75	$67.70
Purchase #6	$63.81	13.333%	$72.3178	$72.32	$72.30	$72.30
Purchase #7	$206.30	7.360%	$221.4837	$221.48	$221.50	$221.50
7 purchase totals =	$572.69		$624.8070	$624.81	$624.85	$624.70