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	$131.68	4.728%	$137.9058	$137.91	$137.90	$137.90
Purchase #2	$31.32	6.746%	$33.4328	$33.43	$33.45	$33.40
Purchase #3	$105.76	11.407%	$117.824	$117.82	$117.80	$117.80
Purchase #4	$195.96	7.611%	$210.8745	$210.87	$210.85	$210.90
Purchase #5	$79.66	4.139%	$82.9571	$82.96	$82.95	$83.00
Purchase #6	$61.97	4.287%	$64.6267	$64.63	$64.65	$64.60
Purchase #7	$52.27	11.139%	$58.0924	$58.09	$58.10	$58.10
7 purchase totals =	$658.62		$705.7133	$705.71	$705.70	$705.70