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	$67.67	6.639%	$72.1626	$72.16	$72.15	$72.20
Purchase #2	$146.39	13.305%	$165.8672	$165.87	$165.85	$165.90
Purchase #3	$153.69	7.508%	$165.229	$165.23	$165.25	$165.20
Purchase #4	$116.36	13.203%	$131.723	$131.72	$131.70	$131.70
Purchase #5	$195.74	11.724%	$218.6886	$218.69	$218.70	$218.70
Purchase #6	$7.79	3.232%	$8.0418	$8.04	$8.05	$8.00
Purchase #7	$73.72	13.842%	$83.9243	$83.92	$83.90	$83.90
7 purchase totals =	$761.36		$845.6365	$845.63	$845.60	$845.60