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	$154.46	3.796%	$160.3233	$160.32	$160.30	$160.30
Purchase #2	$140.32	11.223%	$156.0681	$156.07	$156.05	$156.10
Purchase #3	$232.61	11.564%	$259.509	$259.51	$259.50	$259.50
Purchase #4	$146.38	13.452%	$166.071	$166.07	$166.05	$166.10
Purchase #5	$162.90	10.783%	$180.4655	$180.47	$180.45	$180.50
Purchase #6	$32.75	13.450%	$37.1549	$37.15	$37.15	$37.20
Purchase #7	$6.31	6.124%	$6.6964	$6.70	$6.70	$6.70
7 purchase totals =	$875.73		$966.2882	$966.29	$966.20	$966.40