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	$150.89	10.364%	$166.5282	$166.53	$166.55	$166.50
Purchase #2	$163.79	6.254%	$174.0334	$174.03	$174.05	$174.00
Purchase #3	$150.35	3.691%	$155.8994	$155.90	$155.90	$155.90
Purchase #4	$164.95	9.640%	$180.8512	$180.85	$180.85	$180.90
Purchase #5	$86.54	3.258%	$89.3595	$89.36	$89.35	$89.40
Purchase #6	$20.32	9.803%	$22.312	$22.31	$22.30	$22.30
Purchase #7	$246.70	6.810%	$263.5003	$263.50	$263.50	$263.50
7 purchase totals =	$983.54		$1,052.4840	$1,052.48	$1,052.50	$1,052.50