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	$65.89	6.719%	$70.3171	$70.32	$70.30	$70.30
Purchase #2	$236.65	8.188%	$256.0269	$256.03	$256.05	$256.00
Purchase #3	$36.72	4.380%	$38.3283	$38.33	$38.35	$38.30
Purchase #4	$205.94	9.376%	$225.2489	$225.25	$225.25	$225.20
Purchase #5	$172.86	5.369%	$182.1409	$182.14	$182.15	$182.10
Purchase #6	$151.42	9.135%	$165.2522	$165.25	$165.25	$165.30
Purchase #7	$111.82	7.223%	$119.8968	$119.90	$119.90	$119.90
7 purchase totals =	$981.30		$1,057.2111	$1,057.22	$1,057.25	$1,057.10