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	$55.99	3.384%	$57.8847	$57.88	$57.90	$57.90
Purchase #2	$71.72	6.353%	$76.2764	$76.28	$76.30	$76.30
Purchase #3	$19.30	8.159%	$20.8747	$20.87	$20.85	$20.90
Purchase #4	$190.48	3.337%	$196.8363	$196.84	$196.85	$196.80
Purchase #5	$57.70	9.119%	$62.9617	$62.96	$62.95	$63.00
Purchase #6	$141.54	10.829%	$156.8674	$156.87	$156.85	$156.90
Purchase #7	$64.26	10.829%	$71.2187	$71.22	$71.20	$71.20
7 purchase totals =	$600.99		$642.9199	$642.92	$642.90	$643.00