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	$132.93	4.589%	$139.0302	$139.03	$139.05	$139.00
Purchase #2	$101.46	7.833%	$109.4074	$109.41	$109.40	$109.40
Purchase #3	$188.26	6.199%	$199.9302	$199.93	$199.95	$199.90
Purchase #4	$203.31	12.259%	$228.2338	$228.23	$228.25	$228.20
Purchase #5	$88.87	4.521%	$92.8878	$92.89	$92.90	$92.90
Purchase #6	$159.96	8.739%	$173.9389	$173.94	$173.95	$173.90
Purchase #7	$111.72	10.546%	$123.502	$123.50	$123.50	$123.50
7 purchase totals =	$986.51		$1,066.9303	$1,066.93	$1,067.00	$1,066.80