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	$36.51	13.577%	$41.467	$41.47	$41.45	$41.50
Purchase #2	$185.39	5.857%	$196.2483	$196.25	$196.25	$196.20
Purchase #3	$133.69	4.376%	$139.5403	$139.54	$139.55	$139.50
Purchase #4	$112.74	6.331%	$119.8776	$119.88	$119.90	$119.90
Purchase #5	$36.67	5.683%	$38.754	$38.75	$38.75	$38.80
Purchase #6	$28.67	9.667%	$31.4415	$31.44	$31.45	$31.40
Purchase #7	$234.59	4.642%	$245.4797	$245.48	$245.50	$245.50
7 purchase totals =	$768.26		$812.8084	$812.81	$812.85	$812.80