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	$248.88	12.838%	$280.8312	$280.83	$280.85	$280.80
Purchase #2	$89.27	12.270%	$100.2234	$100.22	$100.20	$100.20
Purchase #3	$238.29	13.367%	$270.1422	$270.14	$270.15	$270.10
Purchase #4	$82.46	4.134%	$85.8689	$85.87	$85.85	$85.90
Purchase #5	$49.59	10.398%	$54.7464	$54.75	$54.75	$54.70
Purchase #6	$102.48	6.533%	$109.175	$109.18	$109.20	$109.20
Purchase #7	$119.86	7.106%	$128.3773	$128.38	$128.40	$128.40
7 purchase totals =	$930.83		$1,029.3644	$1,029.37	$1,029.40	$1,029.30