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	$240.26	3.586%	$248.8757	$248.88	$248.90	$248.90
Purchase #2	$234.86	4.330%	$245.0294	$245.03	$245.05	$245.00
Purchase #3	$5.43	13.763%	$6.1773	$6.18	$6.20	$6.20
Purchase #4	$26.44	7.631%	$28.4576	$28.46	$28.45	$28.50
Purchase #5	$10.95	4.504%	$11.4432	$11.44	$11.45	$11.40
Purchase #6	$34.56	5.663%	$36.5171	$36.52	$36.50	$36.50
Purchase #7	$83.51	7.524%	$89.7933	$89.79	$89.80	$89.80
7 purchase totals =	$636.01		$666.2936	$666.30	$666.35	$666.30