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	$133.29	4.499%	$139.2867	$139.29	$139.30	$139.30
Purchase #2	$167.32	9.814%	$183.7408	$183.74	$183.75	$183.70
Purchase #3	$198.75	4.256%	$207.2088	$207.21	$207.20	$207.20
Purchase #4	$113.89	12.863%	$128.5397	$128.54	$128.55	$128.50
Purchase #5	$123.62	11.577%	$137.9315	$137.93	$137.95	$137.90
Purchase #6	$31.85	11.339%	$35.4615	$35.46	$35.45	$35.50
Purchase #7	$234.39	6.294%	$249.1425	$249.14	$249.15	$249.10
7 purchase totals =	$1,003.11		$1,081.3115	$1,081.31	$1,081.35	$1,081.20