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	$47.47	9.759%	$52.1026	$52.10	$52.10	$52.10
Purchase #2	$44.82	6.846%	$47.8884	$47.89	$47.90	$47.90
Purchase #3	$62.27	8.756%	$67.7224	$67.72	$67.70	$67.70
Purchase #4	$237.71	12.869%	$268.3009	$268.30	$268.30	$268.30
Purchase #5	$162.27	5.726%	$171.5616	$171.56	$171.55	$171.60
Purchase #6	$44.58	7.651%	$47.9908	$47.99	$48.00	$48.00
Purchase #7	$116.46	12.739%	$131.2958	$131.30	$131.30	$131.30
7 purchase totals =	$715.58		$786.8625	$786.86	$786.85	$786.90