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	$29.72	13.632%	$33.7714	$33.77	$33.75	$33.80
Purchase #2	$171.26	9.640%	$187.7695	$187.77	$187.75	$187.80
Purchase #3	$198.67	10.319%	$219.1708	$219.17	$219.15	$219.20
Purchase #4	$147.59	11.500%	$164.5629	$164.56	$164.55	$164.60
Purchase #5	$109.29	3.237%	$112.8277	$112.83	$112.85	$112.80
Purchase #6	$184.82	13.750%	$210.2328	$210.23	$210.25	$210.20
Purchase #7	$38.61	12.357%	$43.381	$43.38	$43.40	$43.40
7 purchase totals =	$879.96		$971.7161	$971.71	$971.70	$971.80