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	$36.77	3.395%	$38.0183	$38.02	$38.00	$38.00
Purchase #2	$62.41	7.471%	$67.0727	$67.07	$67.05	$67.10
Purchase #3	$116.47	10.571%	$128.782	$128.78	$128.80	$128.80
Purchase #4	$250.41	13.755%	$284.8539	$284.85	$284.85	$284.90
Purchase #5	$158.36	10.558%	$175.0796	$175.08	$175.10	$175.10
Purchase #6	$191.48	4.467%	$200.0334	$200.03	$200.05	$200.00
Purchase #7	$99.77	4.816%	$104.5749	$104.57	$104.55	$104.60
7 purchase totals =	$915.67		$998.4148	$998.40	$998.40	$998.50