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	$25.41	9.725%	$27.8811	$27.88	$27.90	$27.90
Purchase #2	$87.62	3.503%	$90.6893	$90.69	$90.70	$90.70
Purchase #3	$77.25	9.283%	$84.4211	$84.42	$84.40	$84.40
Purchase #4	$148.84	8.393%	$161.3321	$161.33	$161.35	$161.30
Purchase #5	$184.65	6.429%	$196.5211	$196.52	$196.50	$196.50
Purchase #6	$43.38	9.223%	$47.3809	$47.38	$47.40	$47.40
Purchase #7	$78.38	9.776%	$86.0424	$86.04	$86.05	$86.00
7 purchase totals =	$645.53		$694.2680	$694.26	$694.30	$694.20