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	$44.36	10.241%	$48.9029	$48.90	$48.90	$48.90
Purchase #2	$197.27	10.674%	$218.3266	$218.33	$218.35	$218.30
Purchase #3	$182.91	7.350%	$196.3539	$196.35	$196.35	$196.40
Purchase #4	$50.37	12.669%	$56.7514	$56.75	$56.75	$56.80
Purchase #5	$18.57	12.242%	$20.8433	$20.84	$20.85	$20.80
Purchase #6	$162.74	11.800%	$181.9433	$181.94	$181.95	$181.90
Purchase #7	$158.49	5.795%	$167.6745	$167.67	$167.65	$167.70
7 purchase totals =	$814.71		$890.7959	$890.78	$890.80	$890.80