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	$154.90	9.678%	$169.8912	$169.89	$169.90	$169.90
Purchase #2	$174.63	7.502%	$187.7307	$187.73	$187.75	$187.70
Purchase #3	$41.60	12.488%	$46.795	$46.80	$46.80	$46.80
Purchase #4	$157.45	12.526%	$177.1722	$177.17	$177.15	$177.20
Purchase #5	$89.96	11.175%	$100.013	$100.01	$100.00	$100.00
Purchase #6	$108.33	7.502%	$116.4569	$116.46	$116.45	$116.50
Purchase #7	$54.37	9.521%	$59.5466	$59.55	$59.55	$59.50
7 purchase totals =	$781.24		$857.6056	$857.61	$857.60	$857.60