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	$90.96	9.310%	$99.4284	$99.43	$99.45	$99.40
Purchase #2	$34.31	9.859%	$37.6926	$37.69	$37.70	$37.70
Purchase #3	$54.99	7.826%	$59.2935	$59.29	$59.30	$59.30
Purchase #4	$168.29	5.122%	$176.9098	$176.91	$176.90	$176.90
Purchase #5	$132.46	5.863%	$140.2261	$140.23	$140.25	$140.20
Purchase #6	$82.88	6.263%	$88.0708	$88.07	$88.05	$88.10
Purchase #7	$86.37	7.181%	$92.5722	$92.57	$92.55	$92.60
7 purchase totals =	$650.26		$694.1934	$694.19	$694.20	$694.20