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	$220.34	6.288%	$234.195	$234.20	$234.20	$234.20
Purchase #2	$239.51	4.287%	$249.7778	$249.78	$249.80	$249.80
Purchase #3	$89.76	4.761%	$94.0335	$94.03	$94.05	$94.00
Purchase #4	$38.71	8.869%	$42.1432	$42.14	$42.15	$42.10
Purchase #5	$9.92	5.576%	$10.4731	$10.47	$10.45	$10.50
Purchase #6	$81.43	4.820%	$85.3549	$85.35	$85.35	$85.40
Purchase #7	$78.35	6.470%	$83.4192	$83.42	$83.40	$83.40
7 purchase totals =	$758.02		$799.3967	$799.39	$799.40	$799.40