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	$67.85	3.360%	$70.1298	$70.13	$70.15	$70.10
Purchase #2	$207.89	11.145%	$231.0593	$231.06	$231.05	$231.10
Purchase #3	$62.79	11.310%	$69.8915	$69.89	$69.90	$69.90
Purchase #4	$181.63	13.747%	$206.5987	$206.60	$206.60	$206.60
Purchase #5	$147.28	13.459%	$167.1024	$167.10	$167.10	$167.10
Purchase #6	$192.54	10.230%	$212.2368	$212.24	$212.25	$212.20
Purchase #7	$48.47	8.342%	$52.5134	$52.51	$52.50	$52.50
7 purchase totals =	$908.45		$1,009.5319	$1,009.53	$1,009.55	$1,009.50