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	$239.63	8.700%	$260.4778	$260.48	$260.50	$260.50
Purchase #2	$97.82	9.410%	$107.0249	$107.02	$107.00	$107.00
Purchase #3	$86.83	8.107%	$93.8693	$93.87	$93.85	$93.90
Purchase #4	$36.35	4.357%	$37.9338	$37.93	$37.95	$37.90
Purchase #5	$53.40	11.850%	$59.7279	$59.73	$59.75	$59.70
Purchase #6	$217.54	9.548%	$238.3107	$238.31	$238.30	$238.30
Purchase #7	$90.75	11.221%	$100.9331	$100.93	$100.95	$100.90
7 purchase totals =	$822.32		$898.2775	$898.27	$898.30	$898.20