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	$152.99	12.363%	$171.9042	$171.90	$171.90	$171.90
Purchase #2	$113.34	5.425%	$119.4887	$119.49	$119.50	$119.50
Purchase #3	$98.83	5.710%	$104.4732	$104.47	$104.45	$104.50
Purchase #4	$113.39	10.224%	$124.983	$124.98	$125.00	$125.00
Purchase #5	$189.73	3.113%	$195.6363	$195.64	$195.65	$195.60
Purchase #6	$98.83	11.186%	$109.8851	$109.89	$109.90	$109.90
Purchase #7	$105.63	5.867%	$111.8273	$111.83	$111.85	$111.80
7 purchase totals =	$872.74		$938.1978	$938.20	$938.25	$938.20