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	$160.41	7.427%	$172.3237	$172.32	$172.30	$172.30
Purchase #2	$59.55	11.443%	$66.3643	$66.36	$66.35	$66.40
Purchase #3	$99.45	4.367%	$103.793	$103.79	$103.80	$103.80
Purchase #4	$184.25	7.535%	$198.1332	$198.13	$198.15	$198.10
Purchase #5	$225.46	5.478%	$237.8107	$237.81	$237.80	$237.80
Purchase #6	$117.29	12.743%	$132.2363	$132.24	$132.25	$132.20
Purchase #7	$77.33	12.220%	$86.7797	$86.78	$86.80	$86.80
7 purchase totals =	$923.74		$997.4409	$997.43	$997.45	$997.40