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	$55.46	7.662%	$59.7093	$59.71	$59.70	$59.70
Purchase #2	$25.72	8.621%	$27.9373	$27.94	$27.95	$27.90
Purchase #3	$162.93	4.302%	$169.9392	$169.94	$169.95	$169.90
Purchase #4	$52.44	9.167%	$57.2472	$57.25	$57.25	$57.20
Purchase #5	$134.73	3.397%	$139.3068	$139.31	$139.30	$139.30
Purchase #6	$175.38	6.591%	$186.9393	$186.94	$186.95	$186.90
Purchase #7	$116.88	10.813%	$129.5182	$129.52	$129.50	$129.50
7 purchase totals =	$723.54		$770.5973	$770.61	$770.60	$770.40