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	$228.28	6.578%	$243.2963	$243.30	$243.30	$243.30
Purchase #2	$227.41	9.462%	$248.9275	$248.93	$248.95	$248.90
Purchase #3	$208.57	3.498%	$215.8658	$215.87	$215.85	$215.90
Purchase #4	$162.50	8.470%	$176.2638	$176.26	$176.25	$176.30
Purchase #5	$39.43	3.692%	$40.8858	$40.89	$40.90	$40.90
Purchase #6	$54.25	10.290%	$59.8323	$59.83	$59.85	$59.80
Purchase #7	$68.98	9.800%	$75.74	$75.74	$75.75	$75.70
7 purchase totals =	$989.42		$1,060.8115	$1,060.82	$1,060.85	$1,060.80