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	$30.52	8.727%	$33.1835	$33.18	$33.20	$33.20
Purchase #2	$85.98	6.337%	$91.4286	$91.43	$91.45	$91.40
Purchase #3	$139.37	12.304%	$156.5181	$156.52	$156.50	$156.50
Purchase #4	$86.47	12.291%	$97.098	$97.10	$97.10	$97.10
Purchase #5	$77.76	11.603%	$86.7825	$86.78	$86.80	$86.80
Purchase #6	$239.27	9.687%	$262.4481	$262.45	$262.45	$262.40
Purchase #7	$90.61	4.291%	$94.4981	$94.50	$94.50	$94.50
7 purchase totals =	$749.98		$821.9569	$821.96	$822.00	$821.90