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	$238.50	7.181%	$255.6267	$255.63	$255.65	$255.60
Purchase #2	$54.96	8.237%	$59.4871	$59.49	$59.50	$59.50
Purchase #3	$110.91	9.457%	$121.3988	$121.40	$121.40	$121.40
Purchase #4	$16.44	13.764%	$18.7028	$18.70	$18.70	$18.70
Purchase #5	$162.57	10.387%	$179.4561	$179.46	$179.45	$179.50
Purchase #6	$126.46	11.367%	$140.8347	$140.83	$140.85	$140.80
Purchase #7	$202.94	12.299%	$227.8996	$227.90	$227.90	$227.90
7 purchase totals =	$912.78		$1,003.4058	$1,003.41	$1,003.45	$1,003.40