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	$94.83	10.614%	$104.8953	$104.90	$104.90	$104.90
Purchase #2	$28.96	11.320%	$32.2383	$32.24	$32.25	$32.20
Purchase #3	$72.66	9.855%	$79.8206	$79.82	$79.80	$79.80
Purchase #4	$48.89	13.377%	$55.43	$55.43	$55.45	$55.40
Purchase #5	$31.89	6.376%	$33.9233	$33.92	$33.90	$33.90
Purchase #6	$23.43	3.365%	$24.2184	$24.22	$24.20	$24.20
Purchase #7	$16.27	7.111%	$17.427	$17.43	$17.45	$17.40
7 purchase totals =	$316.93		$347.9529	$347.96	$347.95	$347.80