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	$49.46	5.563%	$52.2115	$52.21	$52.20	$52.20
Purchase #2	$85.36	6.430%	$90.8486	$90.85	$90.85	$90.80
Purchase #3	$192.65	11.463%	$214.7335	$214.73	$214.75	$214.70
Purchase #4	$38.91	11.667%	$43.4496	$43.45	$43.45	$43.40
Purchase #5	$164.86	3.787%	$171.1032	$171.10	$171.10	$171.10
Purchase #6	$141.47	6.587%	$150.7886	$150.79	$150.80	$150.80
Purchase #7	$133.53	11.413%	$148.7698	$148.77	$148.75	$148.80
7 purchase totals =	$806.24		$871.9048	$871.90	$871.90	$871.80