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	$53.96	4.528%	$56.4033	$56.40	$56.40	$56.40
Purchase #2	$49.48	11.702%	$55.2701	$55.27	$55.25	$55.30
Purchase #3	$163.85	13.467%	$185.9157	$185.92	$185.90	$185.90
Purchase #4	$73.93	11.539%	$82.4608	$82.46	$82.45	$82.50
Purchase #5	$37.99	6.776%	$40.5642	$40.56	$40.55	$40.60
Purchase #6	$211.78	3.290%	$218.7476	$218.75	$218.75	$218.70
Purchase #7	$78.55	3.115%	$80.9968	$81.00	$81.00	$81.00
7 purchase totals =	$669.54		$720.3585	$720.36	$720.30	$720.40