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	$143.64	6.745%	$153.3285	$153.33	$153.35	$153.30
Purchase #2	$223.42	11.684%	$249.5244	$249.52	$249.50	$249.50
Purchase #3	$38.86	8.301%	$42.0858	$42.09	$42.10	$42.10
Purchase #4	$154.32	10.840%	$171.0483	$171.05	$171.05	$171.00
Purchase #5	$238.98	10.840%	$264.8854	$264.89	$264.90	$264.90
Purchase #6	$221.88	12.195%	$248.9383	$248.94	$248.95	$248.90
Purchase #7	$72.75	12.726%	$82.0082	$82.01	$82.00	$82.00
7 purchase totals =	$1,093.85		$1,211.8189	$1,211.83	$1,211.85	$1,211.70