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	$103.31	8.231%	$111.8134	$111.81	$111.80	$111.80
Purchase #2	$66.65	7.163%	$71.4241	$71.42	$71.40	$71.40
Purchase #3	$187.88	9.654%	$206.0179	$206.02	$206.00	$206.00
Purchase #4	$13.42	11.854%	$15.0108	$15.01	$15.00	$15.00
Purchase #5	$85.80	9.766%	$94.1792	$94.18	$94.20	$94.20
Purchase #6	$195.32	13.722%	$222.1218	$222.12	$222.10	$222.10
Purchase #7	$190.90	7.336%	$204.9044	$204.90	$204.90	$204.90
7 purchase totals =	$843.28		$925.4716	$925.46	$925.40	$925.40