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	$68.78	10.871%	$76.2571	$76.26	$76.25	$76.30
Purchase #2	$48.56	6.820%	$51.8718	$51.87	$51.85	$51.90
Purchase #3	$71.32	9.740%	$78.2666	$78.27	$78.25	$78.30
Purchase #4	$119.90	6.851%	$128.1143	$128.11	$128.10	$128.10
Purchase #5	$50.36	9.584%	$55.1865	$55.19	$55.20	$55.20
Purchase #6	$18.73	8.756%	$20.37	$20.37	$20.35	$20.40
Purchase #7	$69.99	12.605%	$78.8122	$78.81	$78.80	$78.80
7 purchase totals =	$447.64		$488.8785	$488.88	$488.80	$489.00