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	$33.92	7.703%	$36.5329	$36.53	$36.55	$36.50
Purchase #2	$42.36	13.211%	$47.9562	$47.96	$47.95	$48.00
Purchase #3	$241.64	3.606%	$250.3535	$250.35	$250.35	$250.40
Purchase #4	$29.98	6.280%	$31.8627	$31.86	$31.85	$31.90
Purchase #5	$205.88	7.209%	$220.7219	$220.72	$220.70	$220.70
Purchase #6	$144.53	11.750%	$161.5123	$161.51	$161.50	$161.50
Purchase #7	$227.59	11.556%	$253.8903	$253.89	$253.90	$253.90
7 purchase totals =	$925.90		$1,002.8298	$1,002.82	$1,002.80	$1,002.90