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	$131.43	8.813%	$143.0129	$143.01	$143.00	$143.00
Purchase #2	$242.26	6.846%	$258.8451	$258.85	$258.85	$258.80
Purchase #3	$24.82	10.672%	$27.4688	$27.47	$27.45	$27.50
Purchase #4	$213.48	12.544%	$240.2589	$240.26	$240.25	$240.30
Purchase #5	$17.73	12.343%	$19.9184	$19.92	$19.90	$19.90
Purchase #6	$124.59	9.566%	$136.5083	$136.51	$136.50	$136.50
Purchase #7	$56.37	5.397%	$59.4123	$59.41	$59.40	$59.40
7 purchase totals =	$810.68		$885.4247	$885.43	$885.35	$885.40