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	$157.96	12.645%	$177.934	$177.93	$177.95	$177.90
Purchase #2	$98.75	10.754%	$109.3696	$109.37	$109.35	$109.40
Purchase #3	$31.55	5.196%	$33.1893	$33.19	$33.20	$33.20
Purchase #4	$165.26	8.284%	$178.9501	$178.95	$178.95	$179.00
Purchase #5	$233.66	9.353%	$255.5142	$255.51	$255.50	$255.50
Purchase #6	$85.67	4.129%	$89.2073	$89.21	$89.20	$89.20
Purchase #7	$171.71	13.516%	$194.9183	$194.92	$194.90	$194.90
7 purchase totals =	$944.56		$1,039.0828	$1,039.08	$1,039.05	$1,039.10