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	$51.27	11.349%	$57.0886	$57.09	$57.10	$57.10
Purchase #2	$181.47	7.397%	$194.8933	$194.89	$194.90	$194.90
Purchase #3	$194.85	10.598%	$215.5002	$215.50	$215.50	$215.50
Purchase #4	$163.43	9.646%	$179.1945	$179.19	$179.20	$179.20
Purchase #5	$142.63	3.696%	$147.9016	$147.90	$147.90	$147.90
Purchase #6	$147.91	9.850%	$162.4791	$162.48	$162.50	$162.50
Purchase #7	$57.74	8.323%	$62.5457	$62.55	$62.55	$62.50
7 purchase totals =	$939.30		$1,019.6030	$1,019.60	$1,019.65	$1,019.60