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	$80.46	11.121%	$89.408	$89.41	$89.40	$89.40
Purchase #2	$136.88	3.686%	$141.9254	$141.93	$141.95	$141.90
Purchase #3	$166.38	13.325%	$188.5501	$188.55	$188.55	$188.60
Purchase #4	$62.28	7.789%	$67.131	$67.13	$67.15	$67.10
Purchase #5	$224.95	11.645%	$251.1454	$251.15	$251.15	$251.10
Purchase #6	$178.55	6.666%	$190.4521	$190.45	$190.45	$190.50
Purchase #7	$221.47	13.593%	$251.5744	$251.57	$251.55	$251.60
7 purchase totals =	$1,070.97		$1,180.1864	$1,180.19	$1,180.20	$1,180.20