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	$137.76	12.162%	$154.5144	$154.51	$154.50	$154.50
Purchase #2	$27.85	13.256%	$31.5418	$31.54	$31.55	$31.50
Purchase #3	$89.44	11.606%	$99.8204	$99.82	$99.80	$99.80
Purchase #4	$65.55	3.524%	$67.86	$67.86	$67.85	$67.90
Purchase #5	$202.50	9.731%	$222.2053	$222.21	$222.20	$222.20
Purchase #6	$56.73	10.817%	$62.8665	$62.87	$62.85	$62.90
Purchase #7	$46.71	8.405%	$50.636	$50.64	$50.65	$50.60
7 purchase totals =	$626.54		$689.4444	$689.45	$689.40	$689.40