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	$99.49	12.432%	$111.8586	$111.86	$111.85	$111.90
Purchase #2	$215.63	11.502%	$240.4318	$240.43	$240.45	$240.40
Purchase #3	$139.81	13.345%	$158.4676	$158.47	$158.45	$158.50
Purchase #4	$6.31	3.432%	$6.5266	$6.53	$6.55	$6.50
Purchase #5	$5.36	11.691%	$5.9866	$5.99	$6.00	$6.00
Purchase #6	$91.26	9.297%	$99.7444	$99.74	$99.75	$99.70
Purchase #7	$131.51	12.628%	$148.1171	$148.12	$148.10	$148.10
7 purchase totals =	$689.37		$771.1327	$771.14	$771.15	$771.10