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	$31.32	3.503%	$32.4171	$32.42	$32.40	$32.40
Purchase #2	$83.80	8.614%	$91.0185	$91.02	$91.00	$91.00
Purchase #3	$91.78	13.837%	$104.4796	$104.48	$104.50	$104.50
Purchase #4	$90.69	9.384%	$99.2003	$99.20	$99.20	$99.20
Purchase #5	$164.64	3.218%	$169.9381	$169.94	$169.95	$169.90
Purchase #6	$96.96	6.664%	$103.4214	$103.42	$103.40	$103.40
Purchase #7	$47.84	10.874%	$53.0421	$53.04	$53.05	$53.00
7 purchase totals =	$607.03		$653.5171	$653.52	$653.50	$653.40