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	$228.96	12.188%	$256.8656	$256.87	$256.85	$256.90
Purchase #2	$36.25	11.158%	$40.2948	$40.29	$40.30	$40.30
Purchase #3	$164.38	9.714%	$180.3479	$180.35	$180.35	$180.30
Purchase #4	$226.61	8.466%	$245.7948	$245.79	$245.80	$245.80
Purchase #5	$131.48	7.367%	$141.1661	$141.17	$141.15	$141.20
Purchase #6	$17.35	9.726%	$19.0375	$19.04	$19.05	$19.00
Purchase #7	$69.45	3.506%	$71.8849	$71.88	$71.90	$71.90
7 purchase totals =	$874.48		$955.3916	$955.39	$955.40	$955.40