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	$53.75	11.396%	$59.8754	$59.88	$59.90	$59.90
Purchase #2	$245.94	11.391%	$273.955	$273.96	$273.95	$274.00
Purchase #3	$73.99	5.821%	$78.297	$78.30	$78.30	$78.30
Purchase #4	$138.34	3.365%	$142.9951	$143.00	$143.00	$143.00
Purchase #5	$18.33	8.582%	$19.9031	$19.90	$19.90	$19.90
Purchase #6	$12.47	7.614%	$13.4195	$13.42	$13.40	$13.40
Purchase #7	$19.89	5.307%	$20.9456	$20.95	$20.95	$20.90
7 purchase totals =	$562.71		$609.3907	$609.41	$609.40	$609.40