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	$71.36	9.778%	$78.3376	$78.34	$78.35	$78.30
Purchase #2	$92.51	5.544%	$97.6388	$97.64	$97.65	$97.60
Purchase #3	$229.88	13.614%	$261.1759	$261.18	$261.20	$261.20
Purchase #4	$77.27	4.459%	$80.7155	$80.72	$80.70	$80.70
Purchase #5	$73.30	8.836%	$79.7768	$79.78	$79.80	$79.80
Purchase #6	$52.61	12.228%	$59.0432	$59.04	$59.05	$59.00
Purchase #7	$191.94	6.844%	$205.0764	$205.08	$205.10	$205.10
7 purchase totals =	$788.87		$861.7642	$861.78	$861.85	$861.70