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	$36.66	11.499%	$40.8755	$40.88	$40.90	$40.90
Purchase #2	$233.61	9.720%	$256.3169	$256.32	$256.30	$256.30
Purchase #3	$228.63	13.681%	$259.9089	$259.91	$259.90	$259.90
Purchase #4	$27.69	9.466%	$30.3111	$30.31	$30.30	$30.30
Purchase #5	$48.32	7.645%	$52.0141	$52.01	$52.00	$52.00
Purchase #6	$25.38	9.271%	$27.733	$27.73	$27.75	$27.70
Purchase #7	$185.93	9.316%	$203.2512	$203.25	$203.25	$203.30
7 purchase totals =	$786.22		$870.4107	$870.41	$870.40	$870.40