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	$150.76	8.820%	$164.057	$164.06	$164.05	$164.10
Purchase #2	$49.77	11.331%	$55.4094	$55.41	$55.40	$55.40
Purchase #3	$63.36	13.459%	$71.8876	$71.89	$71.90	$71.90
Purchase #4	$63.87	9.703%	$70.0673	$70.07	$70.05	$70.10
Purchase #5	$185.55	12.358%	$208.4803	$208.48	$208.50	$208.50
Purchase #6	$14.57	6.121%	$15.4618	$15.46	$15.45	$15.50
Purchase #7	$134.76	11.634%	$150.438	$150.44	$150.45	$150.40
7 purchase totals =	$662.64		$735.8014	$735.81	$735.80	$735.90