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	$56.51	9.332%	$61.7835	$61.78	$61.80	$61.80
Purchase #2	$140.72	11.516%	$156.9253	$156.93	$156.95	$156.90
Purchase #3	$146.30	5.301%	$154.0554	$154.06	$154.05	$154.10
Purchase #4	$47.80	9.768%	$52.4691	$52.47	$52.45	$52.50
Purchase #5	$36.74	12.562%	$41.3553	$41.36	$41.35	$41.40
Purchase #6	$128.55	9.851%	$141.2135	$141.21	$141.20	$141.20
Purchase #7	$54.32	6.548%	$57.8769	$57.88	$57.90	$57.90
7 purchase totals =	$610.94		$665.6790	$665.69	$665.70	$665.80