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	$56.33	4.799%	$59.0333	$59.03	$59.05	$59.00
Purchase #2	$39.93	3.756%	$41.4298	$41.43	$41.45	$41.40
Purchase #3	$38.61	13.789%	$43.9339	$43.93	$43.95	$43.90
Purchase #4	$245.90	6.527%	$261.9499	$261.95	$261.95	$261.90
Purchase #5	$167.96	10.432%	$185.4816	$185.48	$185.50	$185.50
Purchase #6	$135.51	3.565%	$140.3409	$140.34	$140.35	$140.30
Purchase #7	$91.43	6.729%	$97.5823	$97.58	$97.60	$97.60
7 purchase totals =	$775.67		$829.7517	$829.74	$829.85	$829.60