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	$38.96	11.698%	$43.5175	$43.52	$43.50	$43.50
Purchase #2	$129.64	8.227%	$140.3055	$140.31	$140.30	$140.30
Purchase #3	$102.37	6.789%	$109.3199	$109.32	$109.30	$109.30
Purchase #4	$167.86	10.378%	$185.2805	$185.28	$185.30	$185.30
Purchase #5	$203.36	13.369%	$230.5472	$230.55	$230.55	$230.50
Purchase #6	$31.62	8.273%	$34.2359	$34.24	$34.25	$34.20
Purchase #7	$194.72	6.245%	$206.8803	$206.88	$206.90	$206.90
7 purchase totals =	$868.53		$950.0868	$950.10	$950.10	$950.00