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	$25.53	6.499%	$27.1892	$27.19	$27.20	$27.20
Purchase #2	$168.54	6.556%	$179.5895	$179.59	$179.60	$179.60
Purchase #3	$55.45	9.240%	$60.5736	$60.57	$60.55	$60.60
Purchase #4	$134.40	10.337%	$148.2929	$148.29	$148.30	$148.30
Purchase #5	$181.66	9.176%	$198.3291	$198.33	$198.35	$198.30
Purchase #6	$70.62	13.304%	$80.0153	$80.02	$80.00	$80.00
Purchase #7	$143.92	11.801%	$160.904	$160.90	$160.90	$160.90
7 purchase totals =	$780.12		$854.8936	$854.89	$854.90	$854.90