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	$78.50	4.864%	$82.3182	$82.32	$82.30	$82.30
Purchase #2	$218.62	10.189%	$240.8952	$240.90	$240.90	$240.90
Purchase #3	$111.56	7.553%	$119.9861	$119.99	$120.00	$120.00
Purchase #4	$134.25	3.309%	$138.6923	$138.69	$138.70	$138.70
Purchase #5	$245.38	10.263%	$270.5633	$270.56	$270.55	$270.60
Purchase #6	$59.98	9.390%	$65.6121	$65.61	$65.60	$65.60
Purchase #7	$183.94	11.574%	$205.2292	$205.23	$205.25	$205.20
7 purchase totals =	$1,032.23		$1,123.2964	$1,123.30	$1,123.30	$1,123.30