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	$154.96	9.165%	$169.1621	$169.16	$169.15	$169.20
Purchase #2	$229.82	12.815%	$259.2714	$259.27	$259.25	$259.30
Purchase #3	$107.78	11.267%	$119.9236	$119.92	$119.90	$119.90
Purchase #4	$84.98	7.714%	$91.5354	$91.54	$91.55	$91.50
Purchase #5	$17.38	3.756%	$18.0328	$18.03	$18.05	$18.00
Purchase #6	$141.40	13.233%	$160.1115	$160.11	$160.10	$160.10
Purchase #7	$109.90	12.224%	$123.3342	$123.33	$123.35	$123.30
7 purchase totals =	$846.22		$941.3710	$941.36	$941.35	$941.30