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	$123.30	10.736%	$136.5375	$136.54	$136.55	$136.50
Purchase #2	$26.97	8.393%	$29.2336	$29.23	$29.25	$29.20
Purchase #3	$174.98	12.297%	$196.4973	$196.50	$196.50	$196.50
Purchase #4	$49.69	9.141%	$54.2322	$54.23	$54.25	$54.20
Purchase #5	$227.50	6.607%	$242.5309	$242.53	$242.55	$242.50
Purchase #6	$216.63	10.355%	$239.062	$239.06	$239.05	$239.10
Purchase #7	$223.93	11.419%	$249.5006	$249.50	$249.50	$249.50
7 purchase totals =	$1,043.00		$1,147.5941	$1,147.59	$1,147.65	$1,147.50