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	$91.78	8.648%	$99.7171	$99.72	$99.70	$99.70
Purchase #2	$150.38	12.663%	$169.4226	$169.42	$169.40	$169.40
Purchase #3	$25.65	12.808%	$28.9353	$28.94	$28.95	$28.90
Purchase #4	$111.57	7.382%	$119.8061	$119.81	$119.80	$119.80
Purchase #5	$241.30	13.199%	$273.1492	$273.15	$273.15	$273.10
Purchase #6	$105.64	11.434%	$117.7189	$117.72	$117.70	$117.70
Purchase #7	$240.92	6.530%	$256.6521	$256.65	$256.65	$256.70
7 purchase totals =	$967.24		$1,065.4013	$1,065.41	$1,065.35	$1,065.30