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	$77.96	6.517%	$83.0407	$83.04	$83.05	$83.00
Purchase #2	$221.33	6.328%	$235.3358	$235.34	$235.35	$235.30
Purchase #3	$196.55	6.103%	$208.5454	$208.55	$208.55	$208.50
Purchase #4	$56.83	9.773%	$62.384	$62.38	$62.40	$62.40
Purchase #5	$122.36	7.785%	$131.8857	$131.89	$131.90	$131.90
Purchase #6	$72.64	7.843%	$78.3372	$78.34	$78.35	$78.30
Purchase #7	$58.29	13.563%	$66.1959	$66.20	$66.20	$66.20
7 purchase totals =	$805.96		$865.7247	$865.74	$865.80	$865.60