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	$107.71	12.597%	$121.2782	$121.28	$121.30	$121.30
Purchase #2	$135.92	10.477%	$150.1603	$150.16	$150.15	$150.20
Purchase #3	$228.86	9.803%	$251.2951	$251.30	$251.30	$251.30
Purchase #4	$30.82	11.328%	$34.3113	$34.31	$34.30	$34.30
Purchase #5	$98.56	12.726%	$111.1027	$111.10	$111.10	$111.10
Purchase #6	$243.70	10.326%	$268.8645	$268.86	$268.85	$268.90
Purchase #7	$101.72	11.424%	$113.3405	$113.34	$113.35	$113.30
7 purchase totals =	$947.29		$1,050.3526	$1,050.35	$1,050.35	$1,050.40