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	$76.46	8.831%	$83.2122	$83.21	$83.20	$83.20
Purchase #2	$52.81	4.784%	$55.3364	$55.34	$55.35	$55.30
Purchase #3	$139.43	7.588%	$150.0099	$150.01	$150.00	$150.00
Purchase #4	$243.99	10.700%	$270.0969	$270.10	$270.10	$270.10
Purchase #5	$40.76	13.850%	$46.4053	$46.41	$46.40	$46.40
Purchase #6	$239.98	9.807%	$263.5148	$263.51	$263.50	$263.50
Purchase #7	$228.47	13.463%	$259.2289	$259.23	$259.25	$259.20
7 purchase totals =	$1,021.90		$1,127.8044	$1,127.81	$1,127.80	$1,127.70